Are pajamas or a nightgown considered an article of clothing for aveilus?
My assumption is that you mean to ask if an avel is allowed to wear a new pair of pajamas. If it is needed an avel is allowed to wear a new pair of pajamas without having someone else wear them beforehand. This is because the requirement for someone else to wear new clothing before an avel wears it does not apply to simple clothing, such as underwear, because they don’t give a person simcha. Pajamas are considered a simple garment.
Aruch Hashulchan 389-11, The Laws of Aveilus pg. 112.