I cannot recommend you any gold shop, but I can advise you to be
very careful if - or when - you are buying gold and jewelry in Bangkok. Selling these things is one of the most common scams going on among foreign tourists in Bangkok.
You might meet a very friendly person who 'just happens' to have a brother, uncle or relative in the gold business and he will lead you to that shop - and maybe they are okay or maybe they will rip you off, because you don't know enough about gold prices or genuine diamonds/stones. But one thing is for certain... the 'friendly' person will get his commission for bringing you to the shop.
Or you might jump into a taxi or tuk-tuk planning to visit one of the many temples in Bangkok, but the driver will tell you that this particular venue is closed that particular day because of some repairs are going on or there is a service going on for only Thai people - which is, of course, not true!! Instead he will offer you to go to another place - probably for a fair price - but before he takes you there "you must visit my cousin" who 'occasionally' has a gold or juwelry shop. Same story as above... taxi driver will get his commission or gasoline support, and you might get ripped off.
I don't mean to scare you!! But be very sensible and careful what you do!! Have a look on the link below where you can read more about this issue.
2Bangkok.com - The Gem Scam