In the case of Raymarine, I think even their newer transducers require a converter box to use them, so you wouldn't gain any simplicity by getting new ones. If you were to install a standard N2K transducer, you would need a N2K to SeatalkNG converter/cable to put in on a standard N2K network, because Raymarine refuses to use industry standard connectors.
If I purchase new transducers I definitely will not go with Raymarine. Either an N2K transducer or one that connects directly to my Garmin or Simrad.
As far as I can tell and according to Raymarine techs SeatalkNG is 100% N2K compatible at least in the software and communications protocols but they do use proprietary connectors which I find pointless and annoying. Sure it only takes a cable with Ray to standard connectors but still.
But I didn't mean to comment on your choice and reasons - I was responding to the OP's desire to put a N2K transducer directly on his existing network. In his case, buying a new non-N2K transducer plus a converter box seems more trouble than just enlarging his thruhull to take the N2K transducer directly.
Didn't really consider whether you were commenting specifically on my choice or the technique in general but I considered it a kludge from the getgo so not to worry, we're on the same page with that.
It was my first foray into N2K but it added a lot to the learning curve to figure how to get the Raymarine integrated into the rest. All the Garmin and Simrad stuff was 100% standard cable, plug and play. Yes my Ray stuff was previous generation but even new generation takes some messing about to connect.
Don't recall what setup the OP has for plotters but if his existing setup has a transducer connected to a plotter or he can get a cheaper transducer for an existing plotter that is N2K then that could be a cheap and easy solution.