If you want to get off that cold concrete slab now's the time while the building is empty.
Dri-core panels are about $1.25/sf. Or just coat with epoxy floor paint.
https://dricore.com/products/dricore-subfloor/
Nice shop. Looks like you're doing things right - with the possible exception of demolition (sorry about the stitches).

+1 for getting off the cold, hard concrete.
I put down 2" foam insulating board from a big box store, then put Advantech tongue and groove over it. My feet, knees, and back thank me every day for doing so. I'm in Wisconsin and my feet are never cold when I'm in the shop in winter. No issues with rolling heavy stuff around either.
Best wishes on your new shop.