Can I swap a my iPhone 4 camera with a 4S one

only if you swap phones..

No. Different beasts.

Wouldn't you want to switch to a 5s if you did this?

i doubt it would work-they are probably different sizes/shapes and it probably would be a hassle

no...iphone 4 and iPhone 4s is have only similar body but different hardware. Mainboard, processor, battery and also camera. There is no way to replace camera module from iPhone 4s to iPhone 4.
The best way imho is sell iPhone 4 and buy the new phone

Oh go for it and let us know what you find.