I also tend to look at the reviews submitted by Tripadvisor and bookings.com I find the Tripadvisor reviews to be more comprehensive as they can be filtered down to solo reviews.
From my own experience, a solo friendly hotel or complex rests more with the reviews submitted by other solo travellers and with the specific facilities offered by the hotel for adults.. These can include resorts that have adult only pools, accommodation blocks or designated adult only facilities. I also tend to look at the reviews submitted by Tripadvisor and bookings.com I find the Tripadvisor reviews to be more comprehensive as they can be filtered down to solo reviews.