First off welcome to the forum, good to see you're starting with 13th century as I did. Second off what kind of gambeson are you looking for? I got mine custom at Badass Garb, which is at least as good as european outfitters.
Heres my teutonic knight kit, this is period for either the late 12th century or early 13th, the helm probably would of still been used in SOME parts of Germany up to the 1250s as germany tended to hold onto the old styles of armor unlike France or England.
I highly suggest a custom gambeson because if your arming clothes fit well you'll be comfortable in armor, my old gambeson wasnt comfortable under my maille and was a bit tight and hot. Though I would go for canvas as a shell if you got the dome riveted maille as taking it on and off many times might wear linen out quickly, thats the reason I switched to wedge riveted maille, also cause I like he look of it better.
Heres how mine looks and heres where I got it
http://badassgarb.com/Also Matuls is GOOD gambeson maker, I would of gotten one there myself if it wasnt for time constraints from DoK. Padded chausses you probably will have to get custom made as I couldnt find any that would fit me off the rack for my thin stick legs.