Wow, you’re going to get a lot of recommendations!
I did very well for years with a Garmin GPSMap76 and paper maps. Black & white screen, pre-loaded with simple basemap and complete database of bouys & markers. Good battery life on a pair of AAs. Even has a NMEA 183 port I used to drive my tillerpilot. Got me in and out of the shallow bays of Jersey shore, FL Keys, and the 70nm from Key West to Dry Tortugas just fine.
I looked at the color GPSMap 76C / 76CX also, looked like decent units, but I did not like the cost of maps or the small screen. Also, the Garmin 640, which someone else here recommended, looked great, but no output port.
Put the Navionics charting app on my iPhone 3G a few years ago -- OK but slow. Upgraded to iPhone 4S and updated app this year. Wow, very fast, and the compass allows heading-up map orientation.
If you want a handheld of course that’s up to you, however I don’t understand your reasoning about the transducer stopping you from installing a GPS. All you need for a chartplotter is a place to set it and 12 volts to power it. I just put a Garmin 541 on my boat, took about 20 minutes.
When you DO get around to a depthfinder transducer installation, you can put it in the front of a boat using only non-permanent fixtures. On my MacGregor 26S, I set the transducer in the very bow of the boat. I took a little bucket, cut out most of the bottom, and attached it with silicone it to the inside of the hull. The transducer just sat in the water, and “shot” right through the hull just fine. I sail in shallow water a lot, and always liked seeing the depth ahead of me instead of behind.
Best of luck,
Ted