I would get a 10 speed friction shifter. It should pull enough cable for anything, at least up to 10 sp. Just in case you want to change up later. Your rear derailleur would determine the amount. I've used Microshift's 10 speed shifter that does click or friction both road and mountain. I've interchanged them in friction mode. It's my favorite way to shift.
The reason I prefer friction is because once you master all the nuisances, you have zero shifting problems ever again. As long as your derailers are set correctly the only thing that can go wrong is you. I have one bike that has rusted exposed cables. I keep telling myself it needs new cables, but it keeps shifting perfect. Now I want to see just how far they can go without breaking.