You could try the Kingshouse bunkhouse, it's ridiculously espensive for a hostel but better than the hotel. The other thing you could consider is using the bus. I am gradually doing the WHW and GGW as a series of 1 and two day walks. I stayed a couple of nights in Crianlarich, caught the bus down to Ben Glas farm, walked from there to Bridge of Orchy (though I could have stopped at Tyndrum, I was going to see how I felt) and picked up the bus back to Crianlarich. The next morning I caught the bus up to Bridge of Orchy and walked up to Kingshouse. Doing it that way would also solve the minimum 2 nights problem. A surprising amount of the WHW is accessible from the bus that goes down the A82. If you book it they will look out for you rather than speeding past the stop.
I sympathise with you about the camping. I know that carrying the extra weight would detract a lot from my enjoyment of the walk.