I’d agree with JamesO – avoid flying if possible.
Otherwise Spain has a relatively low population and is the most mountainous country in Europe per square mile (seriously!) Otherwise talk to Ash – I’ve ridden in his neck of the woods and there’s some lovely ‘back country’ there without the crowds. Have a look around Morvan region too; it’s well set-up for le VTT although there’s no-one English speaking based there I know of.
Any good guide should cater the riding in your holiday to suit. Go with a reputable company and you shouldn’t have a problem. It could be worth booking a skills course beforehand to get the confidence up too.
As an aside: I guided in the Alps, but every time I go there now it takes me a few days to get my head around the exposure / size /scale of everything. I’d advise taking it easy on your first few days. 😉