Look for armors that come with bodyslide support. Nowadays, most new armors have this option. There's also a bodyslide conversion of all the vanilla armors for CBBE, which is included in CBBE. Changing armors is rather easy: Start bodyslide, create or choose a preset. In the "groups" drowpdown menu, check everything you want to change, then press "build". There are instructions and AFAIK even a tutorial video on the bodyslide mod page.  If you want to convert armors without bodyslide support, you would have to do some work in outfit studio. It's doable, but not that easy. Unfortunately I don't have a really good tutorial at hand.   The bodyslide conversion is for the original version. Only use that and the conversion. You shouldn't use version 2-3 then. I'd suggest trying this first. Maybe it will already solve your issue.  If you want something similar, there's the "Book of CBBE": https://www.nexusmods.com/skyrimspecialedition/mods/13023  Follow the description here - you need to install the original mod for the UUNP body first and then partly overwrite it. Also, should I start a new game for this or should it not matter?