@Ted *******
where did you get your current insurance?
Was it a Thai insurer on the approved list? If so contact them and have them extend the insurance for one added year if possible.
Otherwise you will be stamped into Thailand upon arrival for the time remaining on your current insurance policy and will need to buy insurance from one of the approved Thai insurers for one year and take proof of it to Thai immigration to get a new permission to stay date in your passport.