the BMTA site is only partially useful if you happen to know the system en BKK very well-which makes it obsolete. You first have to know which garage runs a route to find the details.....
Other sites-NONE is uptotdate or really comprehensive-just try.
Bangkok bus, MRT, BTS - All in one Guide
thaitransit.blogspot.com
forum-other modes on
2Bangkok.com | Almost Like Being There (mainly for enthusiasts).
FRom that Big C (is that the 1 behind bangPakOK??) take bus 6-now new shiny yellow- for just 10 bt to the new BTS extension Krung Thonburi and then BTS to Satorn.
(recently the BMTA has re-introduced 7 day and monthly tickets- at 200/800 thb-validONLY in the official govmt. buses-mainly th open red (most are free anyway) and the orange AC+ a few others. Most of BKs citybuses are ''rot ruam''=private bus, these do not accept these tickets
Riverboats (I think a taxi is a hired jitney) leave from behind that BigC ONLY peakhours weekdays-limited stop express.