A beginner / intermediate sailing on small lakes in about 10 knot: Yes, you should look for a board with a dagger (and absolutely NOT an iSonic 125).
A board like the Core 293D will take you from daggerboard lightwind sailing all the way to planing windsurfing and jibes. There are of course other good alternatives as well, like the Phantom Race 320. Or from other manufacturers a Kona One, or a Fanatic Viper, or a RRD Longrider, ...
And you need a sail in the range of 6.5 m2, at least.