Receiving SMS are free.
I've already linked to 90 day, 180 day & 360 day packages in the posts above. But if you don't need Internet, then you don't need a package. Just make a series of 20 baht top ups, at least three.
After 90 days, you can add validity to the SIM thus: https://news-trueid-net.translate.goog/detail/A0y4LppZgBJ3?_x_tr_sl=th&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc&_x_tr_hist=true