T-Mobile Flext-20 with Nokia 6233 - upgrade recommendations?

[FunkyT]

I'm currently on a £15-£20 per month contract (Flext-20) and looking to upgrade (don't mind switching networks).

I make a mix of texts and calls with some internationals thrown in there.

Looking for a decent functional phone - perhaps something like a Nokia 6301.

Thanks for your help!