The only single change airline you have is from Manchester is Singapore Airlines, although they have a sale on, it's not great (£650 ish inc tax) and I think you'll find availability is shot. They did themselves in with a recent amazing sale, and it's a struggle to get anything with them anymore.

So look at a variety of online search engines, and check MAN - HKT, LON - HKT, MAN - BKK and MAN - SIN (Phuket, Bangkok and SIngapore) as you can add on cheap local flights. There is a sale on with Qatar Airlines which means you may get MAN-BKK for under £400 inc tax.

Then check the accommodation accordingly.

What I will say is the single surcharge is a bit of a misnomer. It's just because most people travel as a couple, so Tour Op pricing reflects that, but in reality they get charged a room rate irrespective of whether 1 or 2 people are in it. You won't save the single occupancy surcharge necessarily by DIY'ing, so do doubel check any prices you get and see if a Tour Op will beat it.

Much appriciated Sam