captainsmiffy,
Unfortunatley you can't tamper with the core-OS apps (Mail included). So the only way to re-install is via the iOS re-install.
Mail is normally very stable, I've never seen it crash as described.
I think probably the best chance of resolution for you would be to make sure you have a good backup and then do a full clean re-install of iOS (e.g. via the DFU method... I can point you in the direction of instructions, its a lot quicker and easier than it sounds ! ) and then start afresh... if possible you might want to consider full fresh setup and not restore from backup.
Aside from that, the only other thing I can vaguely imagine is it might be a malformed email in your inbox or something. Have you tried removing email accounts, setting up a test email account somewhere and tried with just that test account ?
You might also have been unucky and had a corrupted iOS upgrade download when you did it ?