There are two stories on a few solicitors websites regarding domicile.
Sir Richard Burton spent the last 17 years of his life living in Switzerland to avoid UK inheritance tax. HMRC considered him still UK domiciled after his death because his funeral instructions were that he be buried wearing a red jacket, holding a book of Dylan Thomas's poems and his coffin be draped in the Welsh Flag.
The other is a financier who moved to Monaco. After he died HMRC found that people familiar with him mentioned that he hated Monaco and spent most of his time in Paris.
With regard to Thailand I suspect it is hard to do unless you have a minimum of permanent resident status. Hard to claim it is your permanent home if you are on yearly extensions of a non immigrant O.
The UK solicitors I spoke to regarding wills, inheritance tax, domicile etc. were unwilling to give a definitive answer other than I would more than likely be considered domiciled in the UK.