The only two companies I can think of that do coach tours are National Express and Wallace Arnold and I'm not 100% sure they do tours of Scotland.
Some years ago my parents were looking at a coach tour and asked me to look up the included hotel at the destination. There reviews were very mixed - 1/2 loved the hotel on one trip and 1/2 hated / loathed it.
Turned out the hotel had two wings - one for 'normal' visitors and the other for coach parties. You can guess which group got which wing.
So having to book your own accommodation may be a good thing.