Central Ratchada: affordable, well connected, and open late
Thailand Cultural Centre sits in central Ratchada, around the arts centre and a cluster of malls that stay open late. The Street Ratchada runs 24 hours, Esplanade covers cinema and shopping, and Jodd Fairs is one stop away. It's an MRT interchange, mostly Thai residents, and considerably cheaper than Sukhumvit for how central it is.
Tell us which unit and we'll arrange a viewing: usually same or next day. 2 months' deposit plus 1 month's rent to move in: no agent fee, and the deposit comes back when you leave.