Before you go down that route, just be sure that you're going to be more comfortable. I know it seems logical, but as someone who's ridden drop bars all my life (I'm 67 now) I find straight bars cause me pain in my wrists. I love mountain biking, but I definitely couldn't do the hours in the saddle that I do on my road bike. I think the suggestions about raising the bars with a suitable stem are a good place to start.