Your old bar ends will rotate separately from the grips, which gives you more flexibility with positioning, so I would stick with them and get the Ergon grips without the ends.

Do you make a fist around the bars when you ride? Try resting your palms on the bars lightly, with your thumbs over the tops of the bars. It is what I do most of the time, and it is much more comfortable.

With the trekking bars, it is worth using the other hand positions, you will develop the confidence to keep your hands away from the brakes.