I carry a 4-person raft from Survival Products (USA). It is light enough for somebody not too strong to lift it. As you say, the big ones are heavy, and in fact some 4-person ones are IMHO too heavy too.
Equipment is IMHO optional. One can buy rafts with a kit of bits like tablets for sickness. Making a mayday call and setting 7700 ought to be enough in most of Europe. I have an emergency bag containing an ICOM radio, a handheld GPS, a 121.50/243/406MHz EPIRB, and some other bits like guaranteed fresh batteries (replace them annually), and would hope that either myself or somebody else can carry that into the raft.
Recently I have been looking at some new American radios, which are immersible, as well as very compact. They are not CAA approved so not for sale in the UK but I will try a covert import via a friend in the USA who will re-package it for me. It should be easy to call up an airliner on 121.50.