“my wife will be with me” will help greatly with budgeting; single men get bankrupted in girlie bars. I would agree with others that 65,000 baht is a sensible budget (or anything between 40-80k). When considering CM do pay a great attention to agricultural burning season as you may need to have extended holidays in the south between February and April due to the smoke. It has been bad … very bad in recent years (anywhere BKK and north of BKK…. It is real health hazard and even civil servants were asked to work from home last February and March).
It is really hard without all the paperwork or an agent … i had just about every document under the sun including one year visa extension yet was refused by two bank branches this week for most minor things on the long term lease and surname before first name on the residence letter from immigration ; 3rd time lucky today when kept trying (and because it was nearing the closing time rushing through paperwork). On a tourist visa not possible on your own. You will need an agent.