A fragrant sachet is usually used in wardrobes. It depends much on your taste - I once had a Brazilian nut that lasted several years, or you can use more "classic" mixtures, like lavender.
For lavender, pick it when it's dark violet, put it in a sachet and it will dry on its own. I sometimes use part of the wooden stalk as well, just cut it into pieces or grind it roughly.
I also use laurel leaves and bays, these as they come straight from the tree, they are very nice and prevent moths in clothes and are much healthier than moth balls! The leaves turn light brown, but will last for years.
Use them as you like - have you have ever tried putting a tiny sachet in your handbag?

You can also make fragrant pillows, but then you must be careful with the herbs you pick. Lavander and rosemary are totally innocuous. When I say innocuous I don't mean to imply that others are harmful, but just make sure you stand the fragrance and they don't give you an allergy! This is a compulsory check if you intend to give it to smeone as a present - make sure they don't suffer from hayfever! Also be sure to have a nice cloth for your pillow or cushion, not too thin so that you don't feel all the sticks and leaves as you rest your head or your body on it!

I would suggest you use a normal cushion, a square one as they are the most common, and possibly one that comes with a zipper, so you don't have to rip it open and saw it back afterwards.... you know, just the easy way, no need to make fancy and complicated stuff unless you are a genius with the needle and have a lot of phantasy...