Based on not wanting too much traffic I would suggest putting these 2 passes on your list Pragel & Grosse Scheidegg (perhaps for another year as they aren't particularly close to Andermatt). They have significant parts that are traffic less (apart from the post bus) or low traffic amounts. Out of the passes I have done these went right back on the list to do again.
I can't say that I am desperately keen to do Lukmanier or Oberalp from the South again. They were ok, just not v scenic or special. Perhaps they are better starting from Andermatt (particularly Oberalp thinking here). Tremola does have quite a few motorcycles on it, but I throughly enjoyed it and would do it again as there weren't a crazy amount on the day I rode it (not weekend I think).
I am a big fan of this website for finding new and interesting passes. There are a lot of small passes that you won't have come across before.
https://www.quaeldich.de https://www.quaeldich.de/paesse/albulapass/karte/
I know its in German, but if you click on a map view for one of the passes and then move the map around with the labels you will find some nice passes or climbs. If you can understand German or are willing to use a translator you can find details of low traffic passes or other climbs that take your fancy. Any time I am going to a new area I check this website out for local climbs. I have found some gems that I would never have thought to try for the exact reason that no one knows them as no one travels on them. As the German name suggest - you could be in a world of pain - there are some crazy steep climbs listed.
Edit: just thought of a pass I have often done and still enjoy: Ächerlipass - I like going up from the Dallenwil side. Again something for another year though as not really good starting in Andermatt.