Regarding x-pens......they do come in different heights. The shorter ones I used for Izzy and Remi are 24in high. I also have 36in pens that keep Stuart in but are harder for me to bend over and pick the dogs out of. They are also heavier to lift onto the back of the rig, etc. Most all the pens do have "doors" in the side of one panel that you can open and close but it is usually easier for me to just lift the dogs at this time. You can see them at Petsmart. You can also find them online at sites like Pet Edge.....compare the prices. Of course shipping cost could make the online deals moot. I think I have even seen them at camping world and Walmart even. If you have any AKC All Breed dog shows in your area, the x-pens are usually carried by at least one of the vendors
You would also get to see all the size/height variations. Good luck.