I moved my expansion tank 35 feet from crawl space to basement. I was told to either move the pressure switch to where the tank is now or buy a buffer tank to put by the existing switch. What size buffer tank do I need?

Honestly, I'd try it first without installing anything. Then, if necessary, I'd just move the switch. Fairly simply undertaking.

As far as a buffer tank, I'm not familiar with that approach, but I would think a fairly small (10 gallon of so) bladder tank would do the job.

I agree it is easier and cheaper in the short and long haul to move the electricity and switch. I just have to drill through the cinder block one more time to get the power into the basement. Thanks for the info