There are different ways of doing it but I would suggest you each get a Non O on the basis of being over 50 from the Embassy in London before you travel. You apply online and you get an e-visa.
This will give you 90 days on arrival in Thailand.
If you’re not sure about accommodation just book hotel or short stay in condo to look around. Don’t commit to long term rent until you’ve tried different areas/buildings.
You can open a bank account each when you arrive. They’ve got more strict so you might need to use an agent just to get your accounts. It should cost just under 4000 baht each.
You’ll need to transfer at least
*****
0 baht into each account in order to get your annual extension of stay.
It needs to stay above 800k for 3 months afterwards and can’t drop below 400k thereafter. It needs to be back up to 800k at least 2 months before the following year’s extension.
It might be easier just to leave the 800k in each account.