I was nervous of not having a “floor” also, so i bought a set of the “grids” that aren’t really grids- they’re solid but are the same size and have the same connectors. I zip tied it all up and it’s super sturdy and I’ve never had a problem!

Editing to add the link! This is what i use as my “floor” and then i put my fleece and bathmats on top. SONGMICS Cube Storage Organizer,... https://www.amazon.com/dp/B079ZTCJ8Q?ref=ppx_pop_mob_ap_share