I have had my softeners for a long time (the current one is a recon of the same type when the original needed repair) so haven't got a recommendation. The Permutit brand-name was bought up by a different company that sticks the labels on machines that are not as good as before.
The local company that delivers my salt also sells, installs and services softeners, so it might be worth trying yours as they will probably service it when needed and hopefully not sell rubbish. The very cheap ones in the DIY sheds are throw-away when they fail. A lot of the better ones use the "Fleck" valve mechanism which is supposed to be reliable.
There are companies that advertise in magazines and will send a salesman to your house. They are generally exceptionally expensive.
Plumbing one in is similar to a washing machine, any professional or DIY plumber can do it. If you know a local plumber you can see if he recommends one (but he will probably just buy it from the local plumbers merchant)
Remember you will have to tip a sackful of salt into it every month or so, so you need good access close to the incoming water main and no stairs. The bags I get are 20kg which is quite heavy. 10kg bags work out more expensive, as do the blocks, but I understand they are very easy to use. You may have a convenient space in the corner of the kitchen under the worktop near the sink, but will need to hinge the worktop oe something to tip the salt in. The machine is very heavy when full so must stand on the floor (not the bottom of a cupboard). Bigger machines hold more salt so need refilling less often. Get a machine with metered regeneration.
If you are thinking about the hard water for drinking tap, you may as well have a small separate tap. Softened water contains tiny extra amounts of sodium, but less than cow's milk and there is far less in a litre of softened water than in a slice of bread.
Your garden tap should be unsoftened because of the cost. Your washing machine and bathroom supplies should be softened because it is so much better.