I’d second arran or mull for accesibility
i think arran is a little bit ‘twee’ but it is picturesque, mull is a lot bigger.
when are you going – mull music festival is a good laugh at the end of april/start of may. tobermory full of folk bands etc. Last time i was there i saw peatbog faeries at the mishnish, the stage is about 2 foot square and theres about 10 of them so they were playing from the crowd – bass player at the bar.
anyway, goat fell on arran is a good hill, but it’s the only one
mull has ben more which is also a good and relatively quiet hill, but there’s plenty more low hills and coastal walks. I’d recommend the walk to the carsaig arches on the south of mull.