What is the best visa option for retirees married to a Thai citizen wishing to spend more time in Thailand?

You could apply for a Marriage Visa but a Retirement Visa (provided that you meet the requirements) involovess mush less hassle.

Can I just say what a wonderful achievement for 35 years married good for you both

You qualify for a Non-O based on Marriage or Retirement, both can be applied for before travelling to Thailand and will give you 90 days on entry. You then apply for a 12 month Extension of Stay (cost 1900B) based on the reason the Non-O was issued by meeting the Thai banked asmount requirement. A re-entry permit cost single 1000B or multi 3800B) allows you to keep your 12 month status live while travelling outside of Thailand.

You could apply for a 90 days Non O based on marriage through the Thai embassy in London before you go, put 400K baht in a Thai bank account two months before you apply for yearly extensions of stays. If you also purchase a multiple re-entry permit you’ll be able to come and go more or less as you like.

Alternatively a Non O based on retirement and bank 800K baht for the first year extension of stay and switch to monthly income for the second year by showing proof of twelve months consecutive transfers of min 65K baht.