Is upgrading from b450 to b550m due to form factor a valid reason?

Hi! I would like some insight on my situation. I've been second-guessing myself and I feel a bit lost.

I've had my pc since around 2018 and I was pretty clueless with pc building at the time-- didn't know that it can go smaller.

Since then, I've had this gigabyte AORUS B450 pro wifi on my current build. Problem is, due to it being an ATX mobo, it's in a huge case (Deepcool Matrexx 55), sitting on my desk taking up a lot of space.

I don't want to set it under my desk due to dust build-up and such-- Additionally as I live with pets as well. I require some more desktop space as I'm making changes to my work area. It feels a bit cramped and the positioning of my second monitor also strains my neck so I only use a half of it.

I have been planning to switch to a smaller build.

If I'm buying a new (matx) motherboard anyway, should I buy a b450m or go for a b550m?

I am currently not considering switching over to am5 right now as I plan to stay on am4 for the long run, since I feel like my pc is adequate for my needs as of now, but I am considering placing my build in a smaller case.

Thanks and I hope I wasn't too confusing!