Peter,i already work six days a week 9 hours a day in a strenuous job
I think that even if you go for the tourist visa and have it granted you will eventually have to make a decision on the settlement visa and it would be better for you to start on addressing that sooner rather then later, no critisism here, just my advice. If you are earning less than £18,600 and you are the commited worker as in the quote above, then, however difficult it might seem, you should start looking towards not just a future with a wife, but also how your career/job can be changed to not just satisfy that, but a later extension of the family too as well as all the things that marrying a Thai lady might involve, money to family, trips to Thailand, even if just for emergencies etc.
It's not easy starting to job hunt, especially working 6 days a week, but IMHO you need to and need to start looking to beat that £18,600 limit, hopefully you will and hopefully it will be by a long way. It won''t be good for you if you do get the holiday visa too and then you have to work all the hours under the sun to pay for the holiday and if your holiday leave gets used up, you'll be left with only Sundays together.
Marrying ain't cheap, and can be even more expensive in our types of situation, you could be under all sorts of stresses and strains that might not currently be a consideration. With immigration costs as well as marriage costs slapped on your wage even £18,600pa might be considered lenient.