Oban is OK - very busy in the season, a town of three halves as it were. A half is very toursity focussed, a half focussed on practicalities and supplying the isles, and half looking like a run-down council estate (as the Scottish West Coast can rather regularly...).
As others have said, if you do not want to eat out then look for accommodation out of town. I personally would look to somewhere quieter, off a main road.
There is so much to do around there - multiple islands that are a day out in themselves such as Kerrera (a lot wilder than you imagine, heaven on a quiet day), Lismore (brilliant community cafe, otter central), Seil, Easdale (very different!), Luing (great community cafe) and for a longer day out, Gigha is a proper slice of heaven on a sunny day!
Mull, if you are into wildlife you have to spend time down Loch Spelve and down to Lochbuie - last time I was there we had two otters, one within a metre of us, 5 golden and a sea eagle overhead within about 15 minutes...Similar with Ulva and Gometra - no cars, so keeps most tourists away, and well worth the walk. Brilliant restaurant on Ulva.
I love Iona, been a few times, but felt last year when I went it was a victim of over tourism with parking for hundreds of cars, 5 coaches at a time arriving, and just crowded around the village. That said, you can walk to quieter bays and get away from the crowds.
Similarly Calgary - a stunning spot, but oh so busy with the instabanger brigade, and a walk away from the main beach was the highlight of my last visit...