I don't have weatherstripping on the door panels but since aluminum is such a good conductor I covered my doors with the good bubble Insulation from Charlie's. Their is not room on the inside door needs to open so I put it on the outside. I live in Northern Indiana and it gets cold here so I have mine well insulated.

The advantage of mortised lock sets is that they will last longer, lever handles won't sag and they offer many more latch/lock functions since the latch bolt and dead bolt are in the same housing and can even be operated together by turning the handle which is why they are standard for schools, hospitals and hotels. For a residential entrance door a mortise set can be set to lock automatically with a button in the door edge rather than in the center of the interior handle (ugh). One style is no more difficult to install than the other if you know how to do it and own the proper equipment. You should be able to buy the door already cut for either set unless you are buying it out of existing stock from a retail store so it is best to deal with a distributor perhaps through a contractor.

You don't need to replace the whole mortise - you can get away with simply replacing the knobs with handles of your liking (of you can buy a pair of JUST modern design handles, not the whole set). I have an old house with all mortises and I've been swapping out some ill-fitting replacement knobs with salvaged knobs that actually fit on the shaft, but I've not been looking at modern knobs. You might want to check out a store nearby that sells door hardware so you can inspect/measure the handles in person. First, find a screwdriver and remove one of the knobs from it (or hold the knob on the other end and unscrew if you see threading) - the knobs will be on a square shaft. Measure the width of the shaft (or square part if it's a shaft with threading). It's probably 5/8". Now you need to find handles that have the same size shaft that is square. Newer knobs and handles screw into the shaft, which is round and threaded at the end, rather than held in place with a little screw in its side. I'm not entirely certain of the shaft compatibility for putting knobs/handles designed for cylindrical sets (modern standard that has supplanted mortises), because I'm not sure if modern handles for mortises are really a thing, but maybe they are.

(keep in mind that on a painted door you have the option of filling and redrilling holes, in case your measurements turn out to be super obscure. but they don't look that odd.)