You won’t get under the bridges on the Fort William to Mallaig road with 14’ 11" trailer, they are 13’ 6" (and there’s 3 of them). Skye to Mallaig ferry used to be notorious for cancellations, check ahead. Also enquire about your height for that ferry, maybe it’s changed but used to be quite a small ferry and not one lorries tended to use but it does sound like your only option.
Avoid A82 Loch Lomond if you can, full of tourists and coaches with a few narrow miles where trucks/buses meeting often bring traffic to a standstill. Easier going up the M73/M9 towards Stirling then turning off M9 onto A84. Couple of blind bends you’ll need to crawl round on that road but it’s nowhere near as bad as Loch Lomond road. Watch your mirrors going up through Glencoe, soft verges with just enough room for 2 lorries to pass on certain stretches. (Reading that back it sounds hellish but it’s not that bad!)
Other than that it’s a beautiful journey though so enjoy!