I'm with BizzyLizzy.
Bonnie is 16 months and I spent the first 14 of them trying to get her to conform to this angelic heel walking ideal that I'd built up in my mind. Not only is it really hard with a cocker as they're not built like that in my view, but it's so boring and unrewarding for them. About two months ago, I popped her Perfect Fit harness on, long line clipped on the back, and we went for a wander round the estate. She would weave about sniffing all the good stuff, get to the end of the line and I would stop. Always a treat for being at my side, and for checking in when we got to a corner. We'd change direction if she was too excited or just for the hell of it. After two months of this, we pootle around happily together, our bond is better, we're outside for longer, she gets the enrichment she needs from scenting everything and I'm relaxed. She's not perfect, and neither am I. But I'm much more in tune with her, know when she's too wound up and we can back off. She's better with all sorts of distractions- I think because she's more exposed because we're outside longer, and because repetition eventually gets through. We are widening the walk to new places, we do 'find it' treats in the long grass, we have a giggle when we pass some poor dog out on a march.
And the funniest thing? When I need her to heel, she does it with a spring in her step, and when I let her off her recall is better. I can get her attention easier when in a new situation too and am noticing her checking in with me for direction when she's unsure. Instead of steam coming out of my ears, I'm much more likely to be heard telling her how good she is.
If I get another puppy, I'm going to skip the torment of trying to get a great heel and do this from the very start.