I would say if you are offering massage the most important thing is to have a couch with an adjustable height - especially if there is more than one therapist giving massages. Doing lots of massage on a couch that is the wrong height for the therapist is almost an instant route to injury and RSI!
Ideally a stationary couch with a foot pump / electric height adjuster is best as then you can move things around for each client - giving them the best pressure possible for each therapist working with them.
Apart from that most couches bellow the £200 mark are about the same. They tend to be foldable / mobile and can only be height adjusted minimally (by moving and re-locking the legs) Post £200 the couches start becoming more ergonomic / have more padding / more bells and whistles, and this is where your foot pump / electric price range seems to begin.
I find one with arm rests and a head rest is the most useful as it means larger clients have space to put their arms without them having to tuck their elbows in to their sides! The head rest helps add a little extra length to the bed for very tall clients, is easy to clean and feels less suffocating than a face hole. I also like couches that have a raise-able end (head end is best) so that the client can be sat up after treatment and come around slowly or clients that dont like laying flat can be raised a little.
Its up to you how much you invest. If there is only one or two therapists giving massage (or they are a similar height) you may just want to go for a mobile / foldable couch for now and see how it goes, it depends how well you think the massage is going to do / what types you want to do (sports massage for example really needs a good bed as there are lots of passive joint movements and moving of the client which rely on a good height on the bed)!