Thanks very much for all your replies. I'm very grateful for all the info.
I think maybe best if I go for the Non O. The thought of being knocked back (however unlikely) at Heathrow, wife in tears etc., is too much of a worry.
The Royal Thai Embassy info/ application seems to have changed since last time I applied. I'm certain before there was a classification for 'travel with Thai spouse' (or similar wording) . Now it's 'Staying with Thai family', which sort of fits - my wife is Thai and is my family! But I'm not really going to Thailand to visit a Thai family who live there. Although we will see her family. I think the previous 'travel with Thai spouse' more truly fitted the situation.
I don't know if I hit on an old page of The RTE, but according to the info I read today, it's saying 30 days tourist entry, not 60! Also the 'Thai family visa' image that I clicked on, sent me to the wrong page.
I guess I had better do the e-visa application as I did a couple of years ago, but I found it a bit of a struggle then, I doubt it's improved and my brain has deteriorated!