Hi.  Upgrading may be the right path for you, but it depends what you want to achieve.  There is nothing wrong with your existing kit, you certainly can connect to WiFi (or buy a Boost, or wire one of your existing Sonos devices).  You could add voice control by buying a few 3rd gen Echo Dots (for example) for very little money.

Just giving you options.

Thanks John. I don’t want to wire any of my speakers: I can live without e’net cables running round the room. I think I’ll look at a Boost, which can replace the Bridge as I understand it. 

That is correct.  Bridges are getting old so it may be best to scrap it. As I said, you don't have to wire anything, although often it is best to do so.

If you get a One SL ($199) it will function as a replacement for the Bridge instead of getting the Boost ($99).

It might be nice to have music near your router or somewhere else easy to wire.

Given that the OP wishes to add voice control, a One may be a better choice than a One SL. The principle is sound, though - if it would be good to have music where the router is, a speaker doesn’t cost a lot more than a Boost.