the Malaysian border has been closed for foreigner since ALREADY IN EFFECT since March 18 - and only allowed "small" border traffic for residents since. And: it is not true that Thailand closed its border. Malaysia made the first step to close its border to Thailand on March 18th. Please stick to facts and don't spread nitwit
as long as flights leave Suvarnabhumi Airport to the U.K. you are advised to do everything to go on stand-by and catch a flight. Only when all options run dry, you have a chance in receiving the "no-fly-help-me-I-am-stuck" letter. . . . . and be told: fligths are still leaving Thailand to the UK up to today
at least you can buy some more time when you apply for the 60 days based on family relations, but you cannot start an application for an EOS with a Non-O based on marriage out of this extension
if you were issued a Multi Entry Non-Imm-O based on marriage, it must be a 1-year visa. Otherwise since you say you got 90 days permitted stay, it must be a Single Entry Non-Imm-O visa. Okay, and "whats about getting extensions of stay" comes down on the finances. For an application for a 1-year EOS you either got the required 400,000 THB on your Thai bank account for 2 months, or you can prove 12 months of money coming into Thailand from abroad 40,000 THB per month. That's the financial requirements next to a few others (proof of marriage status etc)
the boat option is still doable, as is the land border entry into Thailand . . the flight being the seemingly quickest solution, and the land border the "easiest" crossing . . wish you all well . go ahead and don't you worry too much