Get a 50baht sim at some shop like 711 when you land. You should get a few GB. The best deal after that is in my opinion f FINNMOBILE which operates on Dtac network. You can subscribe online with a scan of your passport. Sim is delivered by mail usually 2days later.
🤳🏻My plan is Finn Extreme : 60gb at 100mbps speed, 600minutes and unlimited data at 20mbps (which is still a nice speed and better than most packages suggested here) for 329thb
💸You can get 10thb discount per month with my link :
you can extent your visa excemtion by 30 days for tourist purpose and then again for 60 days for visit Thai wife purpose. That will give you many days. Then do a border hop and do the above again.