Just wanted to say, I don't think you are being shallow at all. We can't deny biology, and what gives us pleasure gives us pleasure. And you are clearly willing to experiment and make an effort to find something that works for both of you. I think a lot of the suggestions above are very worthwhile.
From time to time Lucy wants something more filling than my penis, and I absolutely love using a massive strap-on dildo on her (have looked for extenders too, but haven't really found anything that works well so far). Obviously, this wouldn't be a solution for everyone, and the subject would have to be raised carefully. But if the situation doesn't improve you should probably bring it up in my view; you shouldn't have to struggle in silence, and if he is a real man he will be equally enthusiastic to find something that satisfies you both.
A final quick point is were you with a well-endowed guy in the recent past? Lucy's ex was a fair bit bigger than me, and when we first started going out she was pretty loose for me, but after going out with me for a while she got quite a bit tighter!
Alex.