Tryptophan can indeed boost serotonin and help with sleep. However, it should be taken with caution when combining it with other products which increase serotonin.

Thre are many excellent, trustworthy companies that sell Tryptophan such as Jarrow (http://www.jarrow.com/) , Solray and Life Extension Foundation (http://www.lef.org).

If hypoallergenic products are required, I saw a post on http://www.itsnotmental.com about brands of hypoallergenic products and tryptophan was one of them.