Do I need a transit visa for a 7-hour layover at Suvarnabhumi Airport in Bangkok if I have a single-entry visa for Thailand?

We want to travel to Thailand from India and get VOA. After few days we intend to travel to Cambodia and then head back to India. The problem is, there are no direct flights from Cambodia to India. There is a flight that goes to bangkok and after a layover of 7 hours there's another flight to Mumbai. Now, as our Thailand visa will be for single entry, would we require a transit visa to spend 7 hours at suvarnabhumi airport, bangkok? We will not be leaving the airport and both the flights will be under the same booking, by the same airline and with the same PNR.