I am the queen of letter writing in our marriage, but I write what I know, which is my experience! I couldn't tell you what to write. The only advice I would give is to be direct....no need to sugar coat it all. She seems like a "direct" person in a lot of ways, unless I misread here..
Tell her
1)You are not happy with the way things are 2)You want more (feel free to specifically describe the more: more touching, more laughing, more time spent together doing xyz) 3)You are willing to work to make it better (feel free to say some things you will do/have done like helping around the house) 4)ASK her if she wants more, and what is she willing to do to have more?
If you don't ask, you will never know.
H said the weekend before he bombed me again, "I need to get on livin or get on dyin, one or the other"
Sounds kind of trite, but it is true in some ways. Are you living like you want to be living? You already know that....