Twin XL mattresses are approximately 5 inches longer than standard twins. Standard twins measure 39 inches wide by 75 inches long. Twin XLs measure 39 inches wide by 80 inches long.
The comforter sizes for standard twins and twin XLs are typically the same. According to Bed, Bath and Beyond, they do not usually make comforters specific for twin XL mattresses, but most standard twin comforters will suffice. The standard size of a twin comforter is 68 inches wide and 86 inches long, though certain companies will make oversize speciality comforters.
Some oversize twin comforters may perfectly suit twin XL mattresses. For example, Bergman makes an oversize comforter that measures 68 inches wide and 92 inches long, which could accommodate the extra 5 inches of length. Specialized comforters can be found on various sites online like TwinXL.com or Amazon.
The sheets for twin XL mattresses are more common than comforters since their size is more important. Sheets must fit snugly, unlike comforters that can hang off in either direction. The average size for a fitted twin XL sheet is 39 inches wide and 80 inches long. You must use a standard twin sheet as your flat sheet.