There are some limitations with this type of headset. You generally can't adjust the height of the stem's base very much. I think there are some aftermarket riser adapters, but I don't have any experience with any of them, and I'm not sure how reliable they are. You can really only adjust the angle and the length of the stem, and the angle is limited to some degree (they don't make stems with super steep angles, to really get the bars up high). The adjustable stem type linked by Scooty Puff Jr above will probably be your best bet.
As an alternative example, I'm currently doing up a trekking bar for my Trek 750, because I had a similar desire as you (get the bar further back and higher up).
My bike has a threaded headset with a quill stem, so height is adjustable on this (and I have an adjustable quill stem in it on top of that, so I can adjust height AND angle), but the point I want to make is regarding the design of the bar itself. You can see the main grip areas are some inches back from the end of the stem (almost as far back as being even with the fork steerer tube!). So you have that main grip area, but then the bar also curves back forward, and then there is another grip area AHEAD of the stem. So you can really fine-tune your hand positions and find what's most comfortable to you. I also find that changing my body angle during a ride, in addition to the hand position alone (by moving from the back to the front grip area, for example) is helpful for comfort.
The bar is the same diameter as a standard mountain bike bar (22.2mm), so existing brake levers and shifters are compatible, provided you have enough cable and cable housing to reach your new mounting locations.
Good luck!