I’m in the same position as you. What you need to do is: renew the passport with your current extension stamp, the new passport should have an accompanying letter stating it is a replacement for the one with the extension.
Then go to your local immigration office and ask for them to transfer the stamp to your new passport with said letter.
As far as I have been informed you can not transfer it to your second passport.
When you arrive next week make sure you use the passport with the extension in.
if you get a Wise debit / atm card you can use that for purchasing here. When you have your wise account you can have several different currency accounts. In Thailand I transfer to the Thai wise account in the app, then if I use my card here it automatically deducts from the Thai account. If I’m in Europe I use my euro wise account in the same way.