The temple is in Pracharat Sai 1 Road, Bang Sue. The easiest way to get there is to take the skytrain Silom line to S6 Saphan Taksin station.
Go to the Sathorn pier that is below the Taksin Bridge and take a Chao Phraya river boat, the ordinary service, with no flags, to N23 Wat Soi Thong pier.
The express boats services (with orange and yellow flags) don't stop there.
Careful though, the normal boat service doesn't run on Sundays, it used to.
So take the express boat to N22 Bang Po pier, the pier before the temple pier.
From there take a taxi or tuk tuk to the temple, just five minutes away.
Enjoy your visit.