The basic idea is good. You are thinking about sending some kind of clothing to someone you care for. And, for a 20 to 30 year old boyfriend to send a pajamagram to his 20 to 30 year old girlfriend for Valentine's Day or a "month-versary", it could be fine.
There may be certain situation s for which a more luxurious gift would be more appropriate.
A graduation or job promotion calls for extending congratulations and possibly a gift too, especially when the people involved had worked very hard to reach their goal.
There are very few situations, here, where sending a pajamagram would work. Here's one. A couple married for three years, are very low-key, home bodies. The husband gets a flannel nightgown for his wife who just got her masters degree in December. The gift message reads, "Here's something to keep you warm and comfortable those winter weekend mornings you can now sleep in. Congratulations graduate! Love, …."
Generally, you'd want to make it a bit more upscale when a gift is part of a congratulations. For a young person just starting out with a career, a leather portfolio is a nice idea. High end, fine pens are a good idea too. But keep in mind as with high end watches, people are fussy about them … you need to determine beforehand what they want so they can enjoy and use it.
What do you do for a hostess thank-you gift? You want it to be personal, but not that personal! Getting something for the house is often the right way to go. I love to give things that people may not tend to buy for themselves but would really enjoy using, like fragrant Italian soaps and Irish Linen guest towels or beeswax candles made with essential oils.
There may be, certain people in your life to whom sending a pajamagram would not be very appropriate.
Consider a birthday or holiday gift for your mother-in-law and / or sister (s) -in-law. If you are close, and your relationship is somewhat relaxed, maybe you could send them PJs that are made out of flannel or cotton, and everything would be OK. But, if you aren't that close and your relationship is somewhat formal, they may be a little uncomfortable receiving this kind of gift from you.
Women over 30 would in many cases, regardless of occasion or holiday, want something a little more sophisticated. A beautiful silk scarf gift is a great option here.