This app was mentioned in 1 comment, with an average of 3.00 upvotes
If you want to install proprietary software you should stick with Google Play. Alternatives are much less secure and are the source of most of Android's malware.
I've converted to all F-Droid and you learn to either find workarounds (RSS feed vs news app) or go without. It's a personal decision and since everyone has different wants, needs, and comfort levels what works for some people may not work for others.
Personally, I think banking on a phone is not a good idea even with FOSS. There is an app Bankdroid (F-Droid, Play) which claims to support Swedish banks, that may provide some functionality for you. Although, I have no comment on the app's quality, trustworthiness, or security.
If you want your bank to provide another method of apk distribution you should ask them directly. First party sources are the best option if seeking apps not on F-Droid.