Finnair is OK, but the first flight to Helsinki is classed as short haul so facilities are mundane compared to first flight to Middle East. It’s my favourite route, I fly business class, European food and European stopover.
I don’t know the timing of your first jab relative to your proposed flight. Be careful because I was quite ill after my first jab and wouldn’t have been well enough to fly until about 5 days after the jab. I also had a mild headache for 4 weeks but not enough to take medication for.
After my second jab I felt no effects at all. Personally I’d wait until after the second jab if possible.
I don’t know why Thailands customs and immigration checks has a bad reputation, I suspect it’s caused by people who’ve never been to the Land of Smiles.