I have one of these
the only problem is once they figure they can jump out they can and will try to jump out but if you're supervising then its not too much of an issue
Hamster playpen :Hamster Playpen
They're on amazon. Plastic cnc grids :) https://www.amazon.com/gp/aw/d/B07Q5Y5FQ3?psc=1&ref=ppx_pop_mob_b_asin_title
I use it for my hamster playpen.
lots of carboard boxes cut up in diff ways
I also have a small cat tree
tunnels could also be good addition