First of all, there is no extra risk on eOS. Installing a banking app has the same risk as using a cash card. Don’t store your pin in phone and use app in secure place and everything is fine.
I would prefer try to install your banking app on your unrooted phone. Some banking apps are working out of the box.
If it isn’t working you can it like described in the HowTo’s [HOWTO] Installing Banking Apps
But some banking apps are still not working. Than your online chance is using the webpage of your bank.