If your cats have a scratching pole then they should leave the plants alone. The trunk of a banana is just layers of leaf sheaves. If the cats did damage the outer one the only thing would likely happen is the older leaf would die prematurely. You could then cut off the lead blade but the sheaf would stay and protect the plant.
There are bananas that can be grown from seed, but the commercial ones commonly used for fruit normally have to be grown from suckers. This is a link to a source for banana seeds (Musa species). They have quite a range and are very reliable. Make sure you pick small growing species, will save you a bit of trouble in the long run. I have a purple flowering one which only grows about 1.5 metres tall, ideal for pot culture. And remember to add the height of the pot in any calculations. They are 'greedy' plants, you need to keep them well fed. And they multiply quite readily.
www.rarepalmseeds.com/small.shtml#bananas
