On your way to Koh Samui, stop off at Ranong. Do your border bounce there then head on to either Surathani to get to Samui. Or keep it simple and fly to Kl
Just get your forms when you're at immigration. Some of the tm7 forms you get online are out of date. Just get the photos and photocopy of you passport pages done and take a pen ( blue) and maybe a mask.