The first step is to measure the length and depth. Typically the space in an RV is an odd ball size, and the depth is usually less than sofas designed for residential living rooms. You may need a custom size. You can use any style furnitire that fits the space and your needs, but there are places that specialize in RV-type furniture. Google will find them for you, but here are a couple:
https://restorerv.com/collections/furniture
http://www.glastop.com/rv-furniture-products.asp