You don't need the NKBA 21" minimum on All sides, only the side you are entering or exiting the tub from. On the other three sides I think you would want at least 4" between the outside edge of the rim and the wall so you could clean around it and easily retrieve anything that fell between the tub and wall. (Which is the purpose for the measurement for sinks that do not abut the wall directly).

The WetStyle f/s tub has a removable tray that sits across the tub. I like numberjunkie's idea of a shelf or ledge behind the tub for placing items and also like the idea of having the shower wall next to the tub tiled half-way up to have a space for installing a grab bar. WetStyle has an optional shelf that surrounds the tub, but I think it would make it more challenging to get in and out of the tub - would need to hop over the shelf. The drop-in tub I was initially considering was 72"x42" but that would likely not fit, so would need to be 72"x36". This weekend I looked at an open house (new construction) in my area that had a drop-in tub with a narrow space for the deck surround (see attached photo). The deck was tiled on the top and on the apron with white subway tile. I noticed that with the narrow deck space (about 2") and the tub overhang, it would be awkward to sit on the edge of the tub and swing my legs in or out of the tub. Wiithout space for a deck that is wide enough to comfortably sit on, ease of entry or exit may come down to depth of the tub and options for placement of grab bars. The Wetstyle tub is 22" deep; the drop-in tubs are generally deeper, more like 26"

I have a cast iron clawfoot (I know you said you weren't interested in those specifically) which we love. My husband is 6'5" and has trouble fitting into regular sized tubs; the clawfoot is deep and he can get a good soak. We looked at the Victoria and Albert tubs, but decided on the clawfoot because we found a great deal on a used one on craigslist and it matched the period of our house (1910 bungalow). Neither of us miss having the deck. We are struggling with finding storage, but that is a general issue we are having with the overall bathroom, not specific to the tub. When reading I'll just put my magazine, book or paper on the floor next to the tub. It's not that inconvenient to lean over and pick it up again over the edge of the tub. I don't have any problems getting in and out of the tub, and I've had foot surgery like you would not believe. I've had my ankle, leg, and foot surgically reconstructed 9 times in the past 6 years. While I'm no longer on crutches, I am significantly disabled (makes many DIY projects very difficult for me). I also have very poor balance and suffered nerve damage during one my surgeries so have no sensation on the bottom of my foot. I was warned that all of these issues would make it difficult for me to get in and out of a clawfoot tub, but I just hold onto the opposite side for balance and have no trouble. I have good days and bad days, and on bad days I sit on the edge of the tub and just swing my legs over. I don't think using the clawfoot tub is any more difficult than a regular shallower tub. This was my foot last year, you can see that it was pretty messed up. Even though I had a regular tub during this procedure and only recently got the clawfoot, I'm still recovering from the surgery.

does your bathroom have another heat source? if not, i'd say i'd still want a heater for the odd chilly morning. my shower is in RI and having the ceiling heater (as well as the central heating) keeps us from having to turn up the heat for the whole second floor 'to get it to run' while showering.