What type of visa should I get for teaching in Thailand after accompanying my girlfriend?

Good evening all,

My girlfriend has a job at an international school in Bangkok so is moving there at the beginning of August and already has her visa sorted by her school. The plan is to fly to Bangkok on August 1st then go on a short trip to Siem Reap (5th-8th) before flying back into Bangkok where I will then look for a job (I'm a fully qualified teacher from the UK with a degree/2 yrs experience). I'm just looking for advice on the visa situation.

What sort of visa would be best for me in this situation? Would I need to get exemption on initial arrival to Thailand and then do a border run to get a tourist visa at the start of September... then another border run when I get a job (to convert to a working visa)?

Thanks