Mull is awesome, true sense of the word. Can’t remember what I even did there, just wandered around in the walking boots I think.
We did do a mountain bike ride round the forest heading north from Tobermory (mostly cos that’s where we were). It was good. That was smooth forest tracks and coastline, probably preferable to the roads – I wouldn’t call the roads busy but they are single track all the way.
Even if you’re not a bird/wildlife nut (I am), I’d recommend doing a bit of background reading on, for example, what a white tailed (sea) eagle is, and what other wildlife is on the island because it’ll be all the more exciting when you inevitably see it.
Then you must must take the ‘sealife surveys’ boat tour from Tobermory. Other companies operate tours but these guys are the best. We saw minke whales, seals, otter, harbour porpoise and were very lucky to be chased by dolphins back to the harbour.