Can someone please clarify for me asap?

We are flying back in a week to SE Asia. We will land in Bangkok on May 9, and then fly on to Nakhom Panom May 10, and cross the land border into Thakhek Laos later that evening. We are American. Our layover in Bangkok will be 15 hours. We want to get a hotel in Bangkok while we wait. I'm confused about whether I can still get a visa on arrival at the airport like we do at the borders and what exactly we need to do that. It seems more complicated flying in than it used to, but when we crossed from Laos to Thailand last Dec it was normal easy. I'm just super confused. Any advice asap would be greatly appreciated. Thanks! :)