Try a tenor set; the strings should be slightly thicker. Generally speaking, the lower the open pitch, the thicker the string should be. In particular, you might try the tenor Savarez Alliance strings, which I found to be a little higher tension than most other tenor sets I've tried. But really, almost any tenor-specific set should work, leaving your choice of string brand wide open (and possibly avoiding the need to special order, at least for a quick trial).
I'm a bit biased, but for tone, I think almost any fluorocarbon strings are better than Nylguts. Or try the Aquila Sugars or SuperNylguts (or Lavas). If you want finer control of the tension, Worth makes lighter and heavier sets of their fluorocarbon strings (but don't use browns if you already find the tension too low). Southcoast also sells sets for various tensions, and you can find charts on their website which help indicate which sets to use for the tuning and tension desired for the various standard uke scales.