I've been using laser-cut MDF bases for my minis, for years. I brush on a thick layer of PVA Glue, then dunk them in colored sand mixes, and let it dry. It never warps…
It is made of resin mixed with wood pulp fibers. If you cut it with a saw, wear a close-fitting quality dust mask, to avoid getting the dust in your lungs! The fumes, from a laser cutter, are also bad, but they're typically vented to the outside, so not much of an issue.
MDF is my go-to basing material, even for larger terrain pieces. I used it in 4-inch squares, to base Guard Towers with a pumpkin stem as a cut-off 'tree', with a logged, 'raft' platform on top, as the Guard Tower.
Originally, I used two layers of vinyl floor tiles for my bases. The vinyl warped (the warping can be seen in the base), after a few months, with the same PVA Glue + sand, texturing applied to it. I had to re-base every one of my 12 Guard Towers, and that was a lot of work.
Now I solely use MDF. Could not be happier with the material! All 12 of my Guard Tower bases are as flat as the day I attached them, even after texturing them with PVA Glue and sand. Been flat for many years post re-basing.
If you need MDF cut to specific sizes, smaller than clipboard sizes, I recommend either e-Bay, or Etsy. It can be cut, with superb accuracy, with laser cutters. I order sets in bulk, for my minis.
I needed equilateral triangles of MDF, to make a d20 globe, and I found a seller, on Etsy, who could cut 20 pieces in the exact size I needed, for a modest price -- worked superbly for my project! Best of luck with your projects! Cheers!