The east coast of Mull is mostly very sheltered and lush, cool and damp but mild, very different from the moorland further west.

They have no trouble growing rhubarb in Iceland, so nor will you. The most delicious strawberries I ever ate were grown in northern Norway without the assistance of greenhouses, so you'll grow them too. Icelanders grow potatoes, but of well chosen varieties - they are small but very delicious. Some black plastic to warm the ground before planting and until they come up is a good trick. Redcurrants grow fine in Iceland, but you will be able to grow blackcurrants also I would guess, which are marginal in Iceland. And of course raspberries. I think they also manage to grow some cabbages. Given that you have a mild and damp climate, there is probably a lot more of that ilk that will grow, provided it doesn't require summer's heat.

I'm currently growing a super-early Siberian tomato called Urbikany, maybe even something like that would do you, though obviously it woul dhave to be started off indoors.

Apple tree varieties "suitable for Scotland" are described for example at the Keepers Nursery website. Whether they are suitable for where you are, I cannot say. But I visited an organic nursery in County Sligo, not far inland, which was even growing pears, so there is room for hope.