Lotioncrafter's AromaFix* (INCI: PPG-20 Methyl Glucose Ether) would be a very good choice, but I can't speak from experience about it.
C12-15 alkyl benzoate, an ester that will make your fragrances last longer. I have used this, and I noticed it seemed to make fragrances last longer when I used it at 5% or higher.
Ethylhexylglycerin, an ingredient we find in some preservatives. also helps with fragrances.
Natrasorb Bath can help with bath salts, bath bombs, bath milks, and so on. I use it at 3% and it makes such a huge difference, I've found.
What do I do? I find using my fragrances at 1% in a lotion or slightly more at up to 2% in a rinse off product works well. (I definitely only need 0.5% in my leave in conditioners!) But they don't last all day, and it can be a bit of a punch in the face for a stronger fragrance. This isn't the best advice I can give - the best is to use a fragrance fixative in your products - but it will help a bit.
If you want to know more about fragrance, check out this article I wrote for Handmade Magazine!
What do you do about fragrances in your products? Do you have any helpful tips to share with Catherine?