Hi, Mary,
One of the best hikes my wife and I ever did on Skye (me = mid 60s; wife = early 60s at the time) was from Loch Coruisk to Sligachan. To get to the beginning, you need to take the Bella Jane from Elgol to Loch Coruisk. Once you get off of the boat, cross over the River Scavaig on the stepping stones, and follow the east shore of Loch Coruisk until you come to a path leading up the hill to your right. If you come to a stream, you've gone too far.
Follow the path up the hill. It disappears at times, but it's easy to find again. Your goal will be a saddle between two hilltops. As you climb, you'll see a small lochan on your left. This is Loch a Choire Riabhaich, which feeds the stream that you didn't cross. Once you reach the top. which is Druim Hain, you'll come to a cairn. Turn left at that cairn, and go about 100 yards to the next cairn.
The second cairn marks the start of the path down to Glen Sligachan. From the top of Druim Hain, it's about 5 1/2 miles to the Sligachan Hotel. It's a very well defined path, and the hotel will be in sight most of the way. If there has been a lot of rain, you will probably have a couple of stream crossings. My wife and I made the trek in sunny and dry weather. The Sligachan River had almost dried up. You can reward yourselves at the end of the hike with a meal and a drink at the hotel.
The only really rough patch on this hike is the climb up Druim Hain. It's steep in places, and if you lose the path, you have to make your way across huge flat rock slabs to find your way back. The hike is eight miles. When we made the trip, we had missed the last Portree to Broadford bus, so it was a 45 pound taxi ride. :( I'm pretty sure there is still a Broadford to Elgol post bus, so if you time it right, you can do it all by public transport and boat. If you're staying in Elgol, it makes it all the easier.
There are alternatives to this hike. You can hike to Camasunary from the church at Kilmarie, which is about two miles north of Elgol. You'll be hiking over the Am Mam. Once you get to Camasunary, follow the east shore of Loch na Creitheach, and you'll eventually meet up with the Coruisk to Sligachan path. You can also hike in from Elgol to Camasunary, following the east shore of Loch Scavaig, and then follow the above path through Glen Sligachan.
All of those hikes are outlined on Ordnance Survey Landranger map 32. On all of these hikes, you'll be heading north in Glen Sligachan between the Red and Black Cuillins.
On Mull, the Carsaig Arches is a popular walk, but is difficult. It's eight miles round trip, The hike starts from near Pennyghael, and follows the south shore of Mull. An easier walk would be the Aros Park walk from Tobermory. Some of the best low level hikes on Mull are actually not on Mull. They're on the Island of Ulva, which is accessed by a small ferry (five pounds round trip) from the hamlet of Oskamull on Mull's west coast. There are also some decent walks (not hikes!) on Iona. I'd recommend getting a copy of the small book "Walks Isle of Mull Coll & Tiree," by Paul Williams. It's published by Hallewell Press, and runs around three pounds. I got my copy from Amazon.co.uk.
We're currently planning our 21st. trip to Scotland. We've actually been there more than we've been to our local beach, so you can see that we love the country! If you decide to hire a car, most of the roads that you'll encounter aren't as narrow as those in Cornwall. They've been doing a lot of road upgrading, and also you won't encounter a lot of narrow roads between hedgerows like you have in the south of England. When we started visiting Scotland in the 70s (1970s, I should add), just about every road north and west of the Caledonian Canal was a single track road with passing places. It is so much better now! (But not as interesting. :))
Have a wonderful holiday!