There is a place in Sukhumvit soi 8 before adelphi suite on right hand side, a lady does laundry by weight. I believe it is 40 or 50 bath per kg, and you will get laundry back in few hours. There is also a guy on main Sukhumvit road after soi 8 but you will get it back next day, wash and ironed and same thing 40 or 50 bath per kg. Dont go to any places which charge by piece, it is cheaper to buy clothing in Bangkok than wash it.