Any mattress that didn’t come with the pack n play isn’t safe to add to the pack n play. It can create an entrapment risk for baby. Also, adding anything to the sleep space besides a fitted sheet, a pacifier, and a sleep sack is not safe. That being said…here’s how I made my son’s pack n play more comfortable when he was that age:

This fitted sheet is made by Graco themselves specifically for the pack n play, so it’s definitely safe. It’s quilted with just a little bit of padding to add a cozy layer while still keeping the sleep surface firm enough. I also love Kyte sleep sacks and PJs. They are super soft and cozy. My son slept best (and still does at 2 years old) when he was wearing Kyte sleep sacks and pajamas. Additionally, I used to put a warm heating pad in the pack n play and take it out just before putting my son down for bedtime. It left the sheets feeling nice and warm when he first got in bed.

I also found that having a consistent bedtime routine helps little ones know what to expect, and that creates a safe kind of “cozy” feeling. A warm bath, a book, and their milk in the same order every night helps a lot with creating those sleepy, cozy feelings. So does keeping the room as dark as possible and using white noise.