Sabai as your question indicates means comfortable. In Thai one of the many ways of making a meaning similar to 'very' in English is a double use of the word. This isn't unique to Thai, I believe other Asian languages do the same thing. For example, I think, Tagalog has the same idea. Linguists have a special word for this doubling of the adjective to express the idea of very but I can't remember it off hand. Anyway, using this construction, very good is 'dee dee', very delicious is 'arroy arroy', etc. However, Thai also has other ways of making a word that translates as 'very' for example, the words 'marc', 'jang' and 'loi' all of which indicate 'very'. You can even join them together, for example, 'sanuk jang loi', means very very fun; although 'jang loi' as a way to express the idea of very very tends to be more used by children; adults use 'marc' or even 'marc marc' to indicate very or very very as well as the doubling of the adjective.
I was trying to help my nephew with his English today (today is the first day of the summer holidays in Thailand). He knows the expression 'very good'. I was attempting to get him to say 'very very good' but everytime I asked him to repeat what I said it came back as 'very good very good'. His brain seems stuck in the technique of doubling of a word to express the idea of very or a lot. I guess I'll have to keep working on this with him.