Need Advice on New Chartplotter & Transducer

I have searched and not found any recent discussions on these devices. I have a 1990 22′ Grady White that is currently equipped with a 2005 vintage Garmin GPSMAP 5212 unit with a thru-hull transducer and NMEA 2000 hub. I use the 5212 for finding fish (not so great) and engine/fuel data. The boat is also equipped with a smaller Garmin GPSMAP 546s unit that I typically use for navigation only while I’m looking for fish marks on the 5212. The boat is powered by a 2005 Yamaha 225 4-stroke which I use for trolling, with socks when needed.

I cannot see perch on this unit and based on what I have read online, the technology of my 2005 equipment is not capable of showing enough definition. I am in the market for a new chartplotter and transducer, and possibly a new NMEA 2000 unit as well – not sure I will be able to use the existing one.

I fish for perch and walleye, so I don’t need all the fancy features like side scan and live view, and I don’t want to spend the money on this stuff either. I just want to be able to see marks while underway and then see better definition on the bottom for perch. I would like to keep the 546s connected to the current thru-hull transducer for navigation (and as a backup) if possible, but I am not married to this plan.

I would like advice on which chartplotter/transducer to purchase for just down scan or total scan (I think that is all I need) to find marks at speed and then have better definition while trolling or sitting. I assume a transom mounted transducer will be best, but I am not sure. I will replace the thru-hull transducer if that is the better way to go. Also, do I need to replace the NMEA 2000 hub as well?

Sorry for so many questions, but I am not a techie. Thank you to anyone that can point me in the right direction.