I think its easier if you are totally relaxed, any "big" problems have the annoying habit of jumping into my head at times like that. I only really do it when I'm in bed, all cuddly and warm, just seems to be the easiest time for me.
Sometimes when I regress I do feel an incredible lonelyness , I think I really need a "mummy" to be able to regress fully...
Oh and don't worry about the size thing, it goes sooon enough ;P. I'm pretty much the same, 6'4 and about 280-300lbs :X I just have to be careful not to throw a temper tantrum :S (also its a bit boring having a temper tantrum by your self )