Hej!
There are always threads on here about where to ride in Scotland. If you say what kind of riding you're looking for (the terrain, scenery etc…) and level (technical and physical) then you'll find plenty of suggestions all across the country, as well as the south. The best bet is to have a number of options and wait to see what happens with the weather then plan accordingly.
My girlfriend is Swedish, and when I took here for her first biking and climbing trip round Scotland I designed a trip that I thought would convince her that Scotland was better than Moder Svea. That included riding in some of my favourite places in Perthshire, the Cairngorms, Torridon, Applecross, Skye and the Glencoe area, including a mixture of forest, mountain, and coastal/beach riding at a level that was fun for both of us. If we had had longer than 10 days and more money I would also have included Harris and the Borders, but as it was, (I think) it helped to convert her a little. Since then we've been other places, including the south (and Glentress/Innerliethen- which is definitely fun, and my other Nordisk kompisar have all loved it).
The areas above make a nice tour of the Eastern Highlands and the West Coast, in some of the more spectacular but accessible mountain areas, and you could easily stay longer on one side or the other, depending on the weather. We camped all the time, but you could use hostels or B&Bs in most areas.
We're having a few days off in a couple of weeks, so if you'd like some company for a day somewhere, we might be able to show you somewhere interesting. I'm trying to plan the reverse at the moment, a cykeltur in the fjällhöga nord, so maybe we could exchange some tips?
Anyway, hålla tummarna för vädret, och lycka till med planering. Om ni har frågor eller behöver hjalp med nåt mejla mig (i profil)!