How can I stop extra mass/friction/physics when adding parts to a player's model?

I’m making a game where the player will have models, parts and characters welded to them for accessories and powers, but the issue with this is that these added parts effect the player’s movement and physics in different ways, like increasing friction or causing the player to move to the side when jumping.

I have an animated character model with everything massless checked and having no collision, using a weld constraint to stick its humanoid root part to the player’s root part, I’ve tried using a motor6D for the same effect but it also has the added physics issue. The model has a humanoid, I’ve tried replacing it with a animation controller so it wouldn’t have any states, but this has the same issue.

Any way I can fix this?

sometimes massless doesnt work

put them in an accessory for true massless