Both my girls TT'd late, but did it completely in one go so knickers night and day. They didn't do that until about 3 for DD1 and 3.5 for DD2.

FWIW, and you KNOW I am the wrong one to ask , there is a really good second hand market for pretty anythings, and GF nappies are well supported. You could well find that the money you get back on them when your DS is done covers the costs of the pretties ITMS