How amicable is your relationship with your soon to be ex wife?
If she is willing to help, you could go to Savannakhet now and get a multi entry Non O based on marriage.
By exiting every 90 days, a quick border crossing will suffice, you could continue living in Thailand for a further 15 months as a Non O visa is still valid after divorce.
How long do you have on your current extention of stay? There might be an issue if it's a long time. Consulate in Savannakhet might wonder why you are switching. Other than that, it is a good option.