How would I replace an old mortise lock and entry door set with a new, modern set? Or do I have to replace the door? Would using a door reinforcer help at all? Thanks!

This past fall my wife and I bought a 120 year old Victorian in Michigan. Unfortunately, even with the aftermarket aluminum exterior storm windows, a significant amount of air and heat loss is happening. We determined that it is because of air flowing past the window jams and seams. I looked at getting some of those window plastic shrink rap kits, however each window is over 5 feet wide and about 7 feet high and the ‘large’ window kits are about $8.00 each. With over 15 windows, it would be cost prohibitive. I have been looking into clear plastic sheeting (4 mil) and I was wondering if anyone has just used that, how well it worked, and if that too can be warmed up to shrink a little? At $30 for a roll of 8’ by 100’ it appears that it would be a substantially better deal.