You can't add RAM to the phone. If you activate swapping that won't make your RAM any larger, it just pages data between RAM and SD rather than just clearing RAM when it's needed by another process.
Don't assume that high RAM usage means that you have a problem - that's Windows thinking, and not how unix/linux systems work. I ran a phone with pretty much the same RAM as yours for 3 years without using or needing apps like that.