I also am in the process of switching to trail runners. It's a lot easier to get a fit in a trail running shoes!

And yes, you do need to get another pair. A few hints--shop late in the day when your feet are more apt to be swollen (even better, just after you've finished a hike, if you can work that out). Whether low-cut or "mids," get footwear that is lightweight and comfortable. Take a pack to the store and walk around in the store for at least 30 minutes before you make a decision. Then "hike" with the pack in the carpeted area of your house for a couple of hours, while the shoes are still returnable.