Sleepwear for men is an expanding sector in menswear. There are two basic catagories of mens sleepwear : Woven and stretch. Woven styles can normally be made in just about any factory with basic machinery. Stretch styles however, need to be made using specialist machinery. Mens cotton pyjamas for instance, can usually be made using standard machinery. Mens underpants on the other hand, generally do require special machinery.
It is possible to make rough mock-ups using standard machinery, but these wont have a professional finish and wont have so much stretch. They could be acceptable as a first sample though.