Masses to choose from these days.
Probably a good idea to go down to PCWorld and see how they fit in your hand!
I have several but my current favourite is a simple Logitech Optical Scroll mouse that was about £20 a few months ago. I don't think you'ld go far wrong with a Logitech.
If you want to go wireless, I would suggest one with a recharging station - my last wireless didn't and it ate AAA batteries
You will probably find good prices at your local Tesco, otherwise
www.Novatech.co.uk or
www.Savastore.com.
HTH