Last time I was in DOH on a long layover I was quite easily able to get a quiet 'room' in the AM lounge. The sofas are gigantic, plenty long enough for even the tallest person to be able to sleep on . I think I had to wait 20 or 30 mins for one to open up, but wasn't unreasonable at all. You're limited to 6 hours, but that's generally fine if you're tired when you arrive and just sleep. To each their own, but I found it to be quite sufficient, then just took a shower and went to the restaurant before the next flight.