Similar but not identical situation. UA cancelled my YYZ-ORD flight on a Aeroplan (Air Canada) award. They protected me on a flight 6 hours later but I was going to miss my (same ticket) connection onwards from ORD. I called UA and they said you are SOL, call aeroplan. I called aeroplan and they re-routed my ticket for free onto another carrier from ORD. They were not willing to put me on a non *A carrier nor were they willing to put me on another flight with no award seats which sucks but the flight I wanted had seats luckily.
I am not sure of the exact rule, but I think TG has given you enough warning (by the rules - not a personal opinion of mine or anything
) that they don't have to provide a hotel for overnight. I am sure they'd put you on the earlier TG flight but I doubt they would pay for a change for the non TG flight.
I am not sure if you have been to BKK before / like the city, but IMHO the overnight in BKK is a blessing in disguise. I am here right now, and it really is one of my favourite cities.!