Lots of baby "bookshelf" projects are DIY-appropriate - whether it's book pockets on rods, display shelves, a little wall mounted bookshelf shaped like a house or animal or tree etc.
For sewing, how visual are you? How important are aesthetics? Fabric adds a lot of impact for a small thing. And depending on sales or coupons it can be quite inexpensive .
I found for me it was really easy to make some crib sheets and changing pad cover and a crib skirt to hide the mess underneath - in a few geometric, modern (not pastel "baby") fabric patterns that make the whole nursery look really nice. And cheaper than buying sheets. A lot of bang for the buck there.
The same with a mobile I made with hand sewn little felt animals,, and a walnut bracket out of scrap wood to attach it to the wall.
Stuff like mattress pads to go under the sheet and soak up milk or pee can be cheaper to DIY but wasn't for us (not with the elastic cost).
Blackout lining (or a piece of cardboard behind the blinds) is a worthwhile time investment to DIY. Dark rooms can help so much with sleep :)
By contrast, cribs and dressers and rocking chairs are all easy to buy used... and easy to check if they meet safety standards.