Just had my non-O visa (staying with wife) approved this morning (submitted on Tuesday afternoon, so less than 3 days). Many thanks for the advice on here which was a great help.
By way of returning the favour, here's a full list of what documents I had to upload for applying from the UK, as it's different from the official list, and some of these only catch you out when you get to the very end of the application (especially if you've already transferred all your funds to Thailand). Hopefully this will save someone else some time and stress.
1. Passport biodata page
2. Photo
3. Declaration (you download from the e-visa application)
4. Wage slip or bank statement
5. Wife's Thai ID card
6. Letter from wife inviting you to stay with her at her house (there are examples on the Dutch Thai Embassy website if you Google it).
7. Marriage Certificate
8. Evidence of residency in the country you're applying from (in my case, Passport again)
9. Letter from wife showing you're still married (in our case, we used the same letter from 6 above, as we worded it "I invite my husband, Mr.....")
10. Health insurance to cover $100k
11. Bank statement showing £10k with your name and address
12. Passport pages showing travel details/stamps for the past 12 months
13. Passport again
14. Photo of you holding the biodata page of your passport.
We also found we could only upload one page/document/photo for each answer (so couldn't upload multiple wage slips etc)
Hope this is helpful.