DS (ASD 13) will only wear one particular type of pants - we have 3 pairs which are wearing out fast. They are cotton y-front type, quite thick cotton with no exposed elastic. They were from Marks and Spencer but they no longer make this style in his size. He has latex allergy so can't have elastic exposed. Doesn't like the feel of boxers and insists on the double thickness at the front that you get with y-fronts as opposed to briefs. Sorry if TMI.
I've googled any children's wear shops I can think of but no joy finding what we need so far.
Thank you siver and smile -your links both look along the right lines although he is probably too skinny still for small mens. It wasn't clear from the amazon link what age the sizes s, m and large applied to to but I did a search for "hanes boys briefs" separately and found the ages on the american site (www.hanes.com/Hanes/Products/Kids-Hanes/Kids_Boys-Hanes/Kids_Boys_boysunderwear-Hanes/HB720.aspx) in case anyone else is searching for this in future. So looks like we're sorted!