I was using Simbrief but sometimes it gives wrong NOTAMS - for instance, currently there is a NOTAM for ESSA that RWY 08/26 is CLSD DUE WIP, which is clearly wrong since you can see aircrafts departing RWY 08 on FR24. I also had other wrong NOTAMS, I'm not sure whether it is related to the Data subscription (which I don't have).

I found this on the ICAO website, is it the most accurate source or are there better ones? https://www.icao.int/safety/istars/pages/notams.aspx

for both simming and RL, I use the NOTAM tab in "Avia Weather"-app:

 

For graphical representation I use the splendid NOTAMINFO-site. (mostly for my VFR-trips)
https://notaminfo.com/ukmap

(if you don't want to register for an account but want to see other countries. simply swap "ukmap" to "germanymap" etc.