My post is a visa/travel questions.

I am getting close to retiring and Thailand has its appeals - I am not sure I want to live in the LOS full time.
My plan is to spend 3-4 months a year in the LOS to enjoy the warmer weather and of course the other attractions.

I have a USA passport - On arrival I get a 30 day visa waiver (that is my understanding) and most of my travels over the years have been for 20-30 days. However, now I am looking at stays of 90-120 days.
What are my options? I think I can apply for an extension (?) of my visa waiver - What is the process? Spend a 1-3 thousand baht on an agent and they take care of it?
The other option is to fly to Cambodia or other parts of SE Asia every 30 days but are there issued with immigration coming back into the LOS?

Thoughts on this would be appreciated. If your only thought is Google it - then keep that thought to yourself. I have Googled it and the information is confusing and contradictory. I may get confusing and contradictory answers here but I am happy to hear 1st person experiences from people who actually live and or travel to the LOS