We have used Gala berber carpet in a rental property for years and been very happy with it. It comes as either felt or hessian backed and we have always used the felt back and no underlay We are now planning to use it in our own new loft conversion and weren`t intended to use underlay but, of course, all the carpet shops seem to say we should. These rooms won`t get a lot of use being guest bedrooms. However, it is a bungalow so I wonder if some extra sound proofing in the form of underlay might be a good idea
Felt is not designed for spikes in the gripper like hessian and don't stretch the same as hessian. I always buy cloud 9 underlay and put down before fitters come and I've seen felt carpet over underlay many times, and it's fine especially if held down with furniture it seems