Is there a gel insole you recommend for classic slip ons? Guys, I'm getting really old here and my feet are scrraming at me but I love these shoes too much. Any solutions?

I've tried different vans soles but had no luck. The slip ons are legit what I want to keep wearing and making customs of. My problem is the flatness of the shoe is making my feet hurt now walking in them. I see a ton of third party soles and gel inserts etc on Amazon and in stores so before I embark upon blindly buying some I wondered if this is already something u guys have on lock to help me out. Im an 8 in men's slip ons and 8.5 or 9-9.5 everywhere else. Im used to break ins and non broken in slip ons im fine with that doesnt bother me its the damn flatness that is messing me up!!!!