I’m not as experienced as some people I here but it sounds like you’re doing great!
I just wanted to recommend some wheels that are inexpensive if you’re interested, save you using cardboard.
20cm Trixie Plastic Hamster Wheel (£9.22):
Trixie Exercise Wheel 20cm for Mouse, Dwarf Hamsters Freestanding, Smooth, Quiet 4047974610107 | eBay
^that will be fine for hamsters smaller than Syrian, but main thing to look out for is they don’t bend their back^
28cm Trixie Plastic Hamster Wheel (£12.99):
Trixie 61011 Rotating Ferris Wheel Hamsters, Plastic, ø28 cm, Assortment: Random Colors
https://www.amazon.co.uk/dp/B00365P9...DS0BYZHN0HPXX3
Wooden 21cm (£9.69) and 28cm (£14.49) Trixie Wheel (delivery not added):
Trixie Wooden Exercise Wheel | Free P&P on orders PS39+ at zooplus!
Hope this helps!