Wow! Speaking as someone who only uses cotton in her quilts, YOU ARE A REAL QUILTER. I don't care what fabrics you use.
Okay, that said, there are a few things to consider when selecting fabric:
1) I have seen & carefully studied what has happened to poly-cotton fabrics from 50 years ago. The polyester & cotton fiber eventually start to separate. The polyester is stronger, so it will slightly pull on the cotton over a very long period of time & eventually you will see some of the cotton thread in the fabric start to snap or buckle. I realize that polyester fibers have improved since that time, but it's still going to happen to some extent.
2) Polyester or poly-cotton blends are not recommended for baby quilts because of what happens if they catch on fire. Cotton turns to ash. Poly turns to molten balls of plastic. It typically means the difference between 2nd and 3rd degree burns. (If you use a heating pad while in bed, you also don't want a poly bed quilt.)
3) For longevity, it's generally best to stick with one fiber -- do everything either in only cotton, only wool or only polyester.
4) Polyester fabric & the poly- part of poly-cotton will pill. Cotton doesn't pill.
Polyester is plastic so yes, in a sense it will live forever (just like all those plastic bags floating out in the ocean). But over time with wear-and-tear, stitches will sometimes snap because they seem to bunch up together more in the wash. It seems to be the general consensus that well cared for poly fabrics/threads will last 80 years or so before they start to break down. Well cared for cotton fibers generally start to break down around the 20 year mark.
One other thing... all poly fibers are not the same. I haven't researched them well enough to know how to pick one, but there is information on the web to help understand which types of polyester might be best suited for a bed quilt.
Good luck with your project!