You should not be hitting "different" forehands based on topspin/flat strokes. The difference between flat and top spin shots is the motion of the racquet during the millisecond of contact between the ball and the racquet face (with topspin happenning when the racquet head is rising during contact). As suggested above, even you have terribly loopy strokes, you will hit flat shots if the racquet head does not dip below the height of the ball (since the racquet head is not moving up at contact but, instead, is moving up after contact). So, you should be working on the same stroke, with differences in racquet preparation/finish adjusting the amount of topspin from the stroke.
FYI, I strong believe that every player should hace some topspin on their strokes but I don't recommend extreme topspin (e.g., western grip strokes) for beginners because you will tend to brush up the back of the ball and not hit through the stroke.