Have you considered serviced apartments?
These have all the facilities of a good hotel (restaurant, pool, gym, cable tv, safe deposit boxes etc.) but more room and usually very competitive price-wise. They have either a kitchenette or a decent kitchen with a full-size fridge, rather than the tiny bar fridges in hotels.

Usually such apartments have tv in living room and bedrooms so if you're staying in at night, you don't have to all stay together in the living room.
You could get a 3 bedroom one and all stay together or perhaps a 2 bedroom + 1 bedroom. I think the 3 bedroom might work out cheaper than 2 + 1.
Some I can personally recommend are Somerset (they have several properties around Bangkok - Lake Point, Park Suan Plu, Suwan Park View. I'd rate all of these as 4 star) and Centre Point apartments (they also have several properties in Bangkok - cheaper on internet than their own website.)

If you're interested, you can find these and many more apartments on a number of booking sites and you could start with asiatravel dot com or do a google search for Bangkok apartments and then keep searching the various sites.