If you are working in Thailand full time, why do you want to avoid Thai income tax? Regardless of where your employer is, or whether or not you have an employer, as long as you work, and stay full time in Thailand when doing so, for 6 months a year, then there is really no reason to avoid Thai income tax.
Why is this a concern at all?
It is a concern only if Thailand decides to tax your savings. But so far, there is no indication it is going to do so. Remember, your pension is your savings, not your income. Though this may be different in some countries where your pension is actually not your savings, but somebody else' current tax payment.