OP, here is a thread with discussion of obtaining Non O marriage eVisa in UK.
https://aseannow.com/topic/1315309-non-o-marriage-visa-from-uk-e-visa/
Disregard posts in your thread regarding requirements for extension. That is not required.
Your choice is simple.
Obtain the non O in UK (providing stay up to 90 days) ....OR
Enter Thailand visa exempt + 30 day extension (also covers 90 days)