Boys school trousers??

[Pumpkintopf]

Hi all, struggling with black trousers for DS (13)- he's currently in M&S 15-16 yrs but they're too short on him-though the waist is huge and pulled in with the adjustable elastic things. Problem is 15-16 is the largest size they do except 34W which I'm concerned will be massive on him!
I realise I'm probably being thick but how do I buy school trousers that fit?!
Thanks

Can you not just buy men's plain black trousers in the right waist/hip size? Is he wide, tall or both? Alternatively one of those school uniform shops will have every imaginable size.

I buy the school slim fit chinos from next for my Son who is very slim. My DS is younger, but would be worth a look?

John Lewis trousers are best fit for my DS as the waist is narrower. I've found M&S trousers have become huge around the waist when I've bought them for both DS and DD recently - not sure what's going on with their sizing

Thanks all for the helpful suggestions, appreciate it.

Little update-George (Asda) do age 16-17 trousers in slim fit that are perfect and not as huge on the waist as the M&S ones! Hurray! Only popped in for some milk...😄

Was just coming on to say George ! Cheap too

I used to get BHS They were slim leg and through the hip M&s look like paper bags AND they don't do charcoal grey in younger boys