if tax is paid on the pension in the UK or Australia then no-one will need to pay tax again on transfers into Thailand. The new requirement is to complete a Tax Report.
In theory, the Tax Report will show up tax evasion in the home country or Thailand.
Phuket Muay Thai right on Rawai Beach might be ideal. KYN Phoenix is right on a working fishing beach with really pretty beaches a long walk, short bicycle ride away
KYN Phoenix is on my favourite island but for 2 months the non-Muay Thai activities might be too limited. Good scenery, decent eating places and good boat trips and diving but not much else.
if you're from a country that has a dual tax agreement with Thailand and you have paid the tax due at home you don't have to pay tax a second time when you send it to Thailand even if you declare it.
not sure what tax law change there has been. The rumoured future change for stays of 180 days plus is drafted as a tax reporting change and not a change to any taxes due.
Apart from making a tax report mandatory there will be no other change for people who are currently paying taxes due in their home country or Thailand.