Help please - can/should I upgrade my 3gs from 4.1...?

I have just bought a secondhand jailbroken 3gs. It's currently running 4.1, and was on 6.15.00 (no network) but I managed to downgrade this to 5.13.04, and it is picking up my network fine since.

So my question is, given that most of the apps I'd like to use require at least ios5, what are my options? Should I upgrade to the current ios, through itunes, and is there a way to jailbreak from that yet (I'm assuming that upgrading through itunes will undo my jailbreak?) Or is it possible to download the ipsw for ios5(.xx?) and install that (I used redsn0w before)? Or do I just resign myself to the fact that I won't be able to use most apps?!

Please bear in mind that I'm very much an iphone numpty, I can follow instructions but don't assume any prior knowledge!

Many thanks for any help/advice.

Unless you have the SHSH blobs for the ios5 you wont be able to install them, also because of the baseband firmware you won't be able to use official firmware and you would need to create custom firmware otherwise it will fail the verification and you will be left with nonfunctioning phone.

In other words, doing it through iTunes right now, would kill it. Download TinyUmbrella and see if you can download your SHSH blobs, it should also tell you inside of cydia when you open it whether the blobs are saved or not