Having an install that you do only banking with and lock down very tight would probably suffice.
EG use Firefox+Noscript+Https-Everywhere; don't store any info on disk eg pins, card/acct/branch nums, passwds etc etc.
I also recommend bookmarking the site names and initially enter them manually; don't google them.
Set 'Home Page' to 'Blank'.
Do a minimal Desktop install and keep it updated.
Inside FF, only allow popups and cookies by exception.