@StephenH the IKEA Sonos speakers might be worth looking at for rear speakers, if you are on a budget. The reviews that I've read have been pretty positive.
Don't get them, they are awful. I have one off the bookshelf speakers in my bedroom and it frequently doesn't appear in the app or loses connection when you play things through it. I've moved it into others rooms where I have other sonos speakers and get the same issue with the Ikea one but not the offical Sonos ones. Done the same thing in my bedroom and same result - would never buy them again. The bookshelf also takes up a lot more room as well and the sound quality isn't on the same level.