I don't believe that swanstone makes tubs out of their solid surface material so it would have to be veritek, which gets universally bad reviews for shower enclosures. I am not saying this is a bad tub as I don't know what you're talking about specifically, I'm saying be wary. Another cast iron fan here. We ended up getting rid of our old clawfoot tub (I know, the horror) because it had already been refinished once before by the previous owner and was horribly chipped (the refinish job). Almond and navy blue *shudder* but I digress. It was 3/4 the price to strip and refinish the old tub as it was going to be for a new tub with factory enamel finish. It's our only tub and we have a little boy who likes to bang his toys. I didn't want to have to deal with a chippy mess again so we got a new tub. Do I get brownie points for giving the old tub to the woman who grew up in this house (who lives a block away now)???

I just had a Mirabelle Bradenton 60x32 alcove tub installed on very short notice; had to choose from what I could get shipped that week. Fortunately, these were displayed at several local Ferguson showroom/stores so I could try them out first (Mirabelle is an exclusive Ferguson house brand in the US; this one is made by Clarke though I don't know if they all are). I like it alot; it's a very comfortable, *deep* tub and thanks to the thin sidewalls, it's wider than most inside as well, despite the thin armrests. The backrest is sloped enough to be comfortable but not so much as to steal showering space. We just used a simple Watts overflow from Lowes held in place with a single screw; it can be detached, reinstalled upside down with the drain slot facing upward rather than at the bottom, and you get two inches of added depth that way. American Standard sells priceier replacement "deep soak" overflows that are designed to look good with the drain slot near the top. Anyway, my only complaints with the tub are that they could have made it an inch or two longer at the drain end (not a problem for you it sounds like) and the armrest is a bit higher than I'd prefer - it is at a good height to use whilst sitting up rather than lying down in the water. This is designed for a single bather, but two could squeeze in if in the same direction both on your side, if you're reasonbly small. It would be a tight fit but may suffice for occasional use. There's definitely more room inside than most tubs with the same exterior length and width. As for whether 2 can fit in a 34"w tub; usually not unless it's a single-walled freestanding tub which is almost as wide on the inside as out, or is very long so you can stretch out or sit across from each other. Kohler makes a "Tea for Two" 60"x32" alcove tub designed billed as the only 5-foot replacement alcove tub that can accommodate two people, but that's a stretch; those who've installed them say to better plan on one at a time, name unwithstanding. I've found some 36" wide tubs that will fit two comfortably, both side by side or at opposite ends; 66" or especially 72" lengths help alot here, as do double-ended designs that place the faucetry in the center, but for both facing the same way an end-drain tub can work too, and they have the benefit of more foot room at the bottom of the tub. An apron is a panel found on some alcove tubs that negates the need for a wall of tile or other material on the outside of the exposed tub wall. It's often built in, but sometimes an extra-cost option (espcially with whirlpools and air tubs). Some drop-in tubs have optional aprons as well as optional tile-in moldings. Here's an example of a tub with a front apron:

First of all, if the DWV(drain,waste & vent) piping is installed correctly there should be an adequate pitch to insure there is never any standing water in the pipes so freezing is basically a non-issue. The exceptions to this would be P-traps which may be below the sub floor such as under the bathtub, shower stall or laundry standpipe. In this case the P-traps will generally be well up in the joist bay and very near the underside of the sub floor. General purpose insulation can be installed in the stud bay on the underside of the trap but do not insulate the top of the trap. Keep the top area open so that residual heat from the living space above can come through the sub floor and maintain a minimal temperature in the joist bay in the proximity of the P-trap. Water supply lines are a whole different problem. We must keep in mind that insulation does not generate heat, it only retards the rate of heat loss. Even well insulated supply pipes will freeze if exposed to sub freezing to sub-zero temperature for a prolonged period of time. One method of protecting the pipe is to run it as high as possible through the joist bays and insulate the underside in the same manner as suggested for P-traps. Another method is to run the hot & cold lines very close together, then install a circulation loop on the hot water line and cover both the hot & cold lines in a common insulation. In this manner the slight amount of heat radiating from the hot water line would be retained in the common insulation and thereby protect the adjacent cold water line. The next option would be to install thermostatic controlled electric heating tapes on the pipes, then cover that with insulation to keep the heat in. In regards to what type of insulation. It really doesn't make a lot of difference. While the preformed poly-foam insulation is what the homeowner is usually most familiar with, they make both poly-foam and rigid preformed sections of fiberglass pipe insulation with either a paper or plastic covering in sizes ranging from 1/2" diameter up to 20" diameter and they also make matching preformed covers for Tee's and elbows but you would have to get those types of insulation from a local HVAC or Plumbing Supply.

I could be wrong (but I doubt it), but the 72" x 42" tub noted above, if properly installed, will take up more space than 72" x 42" (see installation guide). I suggest the OP first determine if a two person tub is a need or a desire. If it is a need, then she should seek advice for a solution from the "design architect" or a local licensed architect if the "design architect" is not licensed. From what I can tell from the fragment of the bathroom's floor plan provided, it is not designed as a bathroom fitting for such a grandiose tub. It appears that there was a communication failure in both directions.