The main thing is to avoid Jakarta.
I also support Raja Ampat. When I booked my trip a couple of years ago, hadn't even crossed my mind until August. Not only did I get on a good boat, but happily had my own room as did every other solo diver that showed up. There were only twelve of us on a twenty passenger boat. Word must really be getting out because I've been looking to return in January last year and this upcoming and there's "no room at the inn". Still, I believe if a single diver is able to be completely flexible on their schedule, you'll get a spot.

I also support Raja Ampat. When I booked my trip a couple of years ago, hadn't even crossed my mind until August. Not only did I get on a good boat, but happily had my own room as did every other solo diver that showed up. There were only twelve of us on a twenty passenger boat. Word must really be getting out because I've been looking to return in January last year and this upcoming and there's "no room at the inn". Still, I believe if a single diver is able to be completely flexible on their schedule, you'll get a spot.