What kind of hamster do you have? Sometimes with dwarf hamsters, I find that they prefer a covered wheel instead of an open one. Like this:
https://www.amazon.com/Exotic-Nutrition-Silent-Runner-Wide/dp/B01B15GZ1U

I'm not saying you need to get this exact wheel but one with a cover plate might make him feel more comfortable.

Also, I'm glad you are thinking of upgrading but don't get too caught on on minimums. Here is an article about cage size: https://hamsterclubhouse.com/forum/viewtopic.php?t=89

and some lists of cages available (by country):
https://hamsterclubhouse.com/forum/viewtopic.php?t=46