Let me tell you a couple of things about the slider.
First, contrary to what a lot of people have been saying (no doubt because they themselves don’t know how to throw it!), the slider, when thrown correctly, is easier on the arm and shoulder than just about any other pitch, and many pitchers who have trouble with the curve ball—as you seem to be doing—will find the slider easier to work with. I was a true natural sidearmer, and I learned the pitch at age 16 from my pitching coach who was a key member of the Yankees’ legendary Big Three rotation of the late 40s to the mid-50s. His name—you might remember it—was Ed Lopat, and he threw a very good one (both 3/4 and sidearm), and here’s what he told me: "Throw it like a curve, but roll your wrist, don’t snap it."
Lopat used a very much offcenter grip, with the index and middle fingers very close together and the middle finger just touching one seam. He demonstrated the wrist action, which in my case would be an easier version of the karate-chop I used for my curve ball—and then he just handed me the ball and said “Go ahead, try it.” I got the hang of it in about ten minutes, but I knew that this wasn’t going to be one of those pitches I could use right away, so I spent some months working on it and refining it. In August 1952 I felt comfortable enough with it to try it in a game, and I did just that—coming into a game in relief in the seventh inning when our starting pitcher had to leave the game because of a nasty blister on his pitching hand—and the situation was this: bases loaded, one out, our lead had been cut from 6-0 to 6-4, and I would be facing a dangerous pinch-hitter. I got the guy on three sliders, the third one being a crossfire which I used all the time, and the dumb cluck never took the bat off his shoulder, just stood there and went “duh” as that pitch broke sharply over the plate! I got the next batter—this is a story in itself—and pitched two more scoreless innings; we got our three runs back and won 9-4. In my next two starts I got solid confirmation about that slider—that was my strikeout pitch!
I think you would do very well with it. I would advise you to find a good pitching coach, preferably one with professional experience (high minor leagues at least), and have him teach you how to throw it correctly. I have seen many major league pitchers over the years do very well with a fastball-slider-changeup combination; they don’t even need a curve ball. I remember another Yankee pitcher—Vic Raschi, a fireballing righthander who had an even more devastating slider and a very good change; he didn’t have what they used to call Aunt Susie, and he didn’t need it. And one more thing—here’s a very interesting variation of it that Lopat told me about: you use a knuckleball grip and throw the slider with it. It breaks bats and gets delicious outs. 
8) :baseballpitcher:
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8) :baseballpitcher: