Nickel F strings seem to be pretty tough to find. For some reason, there are a lot more options in stainless. Anyway, GHS makes a .20 Boomer that balances well. I get mine here:
http://www.juststrings.com/
I've been using the standard Roscoe set for a while now, which I believe are D'Addario nickels with a Dean Markley f, and I haven't had any balancing issues. The only issues I've ever had, was when I tried using
unwound F strings.
If you wanna deaden your current F string though, try rubbing some cooking oil, butter, crisco onto it. That should deaden it right up. Just make sure you clean it before you put it back on your bass!

I would try the Boomer F string first, though.