While I've no idea how much work it takes to do any of this, I keep thinking that there are a number of different Bear specie, and while they vary in size significantly, their general appearance, other than color, is quite similar.
So what if there were Black Bears, Brown Bears (what's in game) & Polar Bears. Maybe even Cubs.
Green Forest mostly Black Bears. Roughly half the size of Brown Bears. Could ramp difficulty with 'mother and her cubs', or mix in more Browns.
Snow would get Polar bears of course.
Wasteland has Zombie bears.
Possibly Zombie Black bears for Burnt Forest, and maybe a lighter pelt on those for the Desert? "Blonde" Black bears are a real thing and that'd let them blend into the desert, similar to the Cougar.
Just thinking that, maybe, this wouldn't be weeks of work, and it would seem to support the future intent of making the tougher biomes tougher, and add some variance to animal dangers.
Edit: having smaller Black bears (or cubs) might mean they could fit through normal doors, so would increase their danger lvl, even if they might have less HPs.