This is what I use for EC: comfy potty. I use the white bowl and the blue ring, and toss out the base. By the time my kids are ready for a potty they sit down on and use independently, the opening on this one is way too small for their butts and assorted boy parts to fit down in! But the comfy bowl part is just right for ECing a baby younger than 6 mos, in my experience. The butt fits down inside (sometimes you have to reseat a boy so the penis gets down too, I bet it's even better for a girl!) and the baby can sit for a while without getting uncomfortable. The bowl tapers down and is just the right size and shape for me to hold in my lap and nurse while he's on it.
Now, the reviews on it are terrible... and they're not exactly untrue. But I am obsessed with comfort for my babes, and the blue foam ring makes for the cushiest potty around! The problem is that if pee gets in between the ring and the bowl and is allowed to sit there, the ring will soak it up. It's like a sponge. So after a while, you have a stinky ring! I have found that if I rinse out the bowl and then wipe dry both the ring and the rim of the bowl where it sits, I don't have an issue. I love this potty for ECing a little baby.
As the baby gets to be about 6 mos and able to really sit up, I use something like this seat (mine has handles) on the toilet. And I use the sink a lot more once they stop wanting to nurse while pottying- with boys I just can't seem to get things aimed into the sink right while they're nursing!