If you're looking to get a pocket door window replacement then you'll want to consider having a rough opening done by a local contractor. With a rough opening installed, the actual size of the pocket door will be slightly larger than the actual size of the old single hung window. Now, depending on what you're replacing the window with, you may need a full frame installation or just the pocket doors only. There are many contractors that will be able to install both types at no extra cost to you, so if you don't have a lot to spend on this project it may be a good way for you to go.
When choosing the windows that you want to use for your pocket-type doors, you need to remember that you are going to need plenty of room for the installation. One of the easiest styles of these windows to find is called pocket-ford replacement windows. These are one of the newer replacement windows and they look very nice. Now, if you're looking to go with a more traditional or classical look you will find that your choices are more limited. If you're looking for more modern or contemporary style windows you will not be able to find a wider range of options.