I'm having a problem with baking multiple textures.

This is a little hard to explain, but I’ll try my best.

I have a low-poly model, that I want to make the polygon count even lower, I thought a good way to do this, is instead of making the clothes as separate models, just have them as part of the texture, and I figured an easy way to do this is by baking the textures of the clothes I have already made into the body model.

So I made a duplicate of the body model, make a smart UV, and a new image, ready to bake the textures onto, baking the original model into the copy was no problem, but when I try to bake the clothes textures onto that, I get problems.

When I try to select all of my clothes (and the original body model) and bake them all on at once, it only bakes on the body model’s textures, and if I try to bake one of the clothes onto it, it bakes it on, but messes everything else up, for example, if I bake the textures of a jacket onto the model, the jacket textures appear on it, but the rest of the body’s texture (head, legs, etc.) gets all messed up!

Here’s what I mean:
Here’s how my model looks like without any cloth textures added:

Here’s how it looks after I try to bake one on (notice :

I’ve tried everything to solve this problem, I’ve made sure I had “select to active” enabled and “clear” disabled, and also that the bake is on textured mode at all times.

Is there anyway to actually just bake textures on top of others, and have it just append the active texture, rather than replacing or messing it up? If not, is there anyway at all to bake multiple textures into one?