It's very normal and okay for a 13 year old boy or anyone of any age to want to wear diapers for any reason including comfort.
I find diapers very comforting myself and they help me relax.
I've loved wearing diapers since around age 5 and have worn diapers for comfort and for fun at 13 years old as well.
There are many other 13 year old boys and other kids and teens and adults who also love wearing diapers.
You're certainly not alone.
Although I do remember thinking I was alone in my loving of diapers but I was really surprised to find out I was not and it made me feel even better.
You can order disposable adult diapers online or Youth Disposable diapers online which will fit you and the diapers will ship discretely.
However if you cannot order diapers online then you may be able to fit into a Dollar General Gentle Steps size 7 diaper.
They are very good diapers and are pretty cheap and very squishy as well.