You also have to take into consideration all the other improvements in tech over your current tv. The difference will be huge for you. Resolution is just one part of what makes a picture good. Since you are so on the fence, wait till black Friday or Super Bowl to buy your tv.
Also there are going to be a bunch of 1080p tvs with HDR this year. I think all of the Sony ones will have them. If you are still rocking 720p you might as well go 4k though since you don't seem to upgrade your tv often. HDR is a big fucking deal and if set up correctly you will notice a huge difference.