its super easy to get vpn’s. Just be careful to research for good, reliable and trustworthy providers.
You can get some free, and pay for others, but look around on the internet for reviews and recommendations/common providers.
The bank who log into will be able to access your IP address from your communications with their electronic data systems, and ip addresses have locations, but I’m not sure what you’re saying about your ex-partner gaining this information?
At what point do you think your ex will be able to access your ip address from you logging into your joint account?