The Yepp Mini should be compatible with any quill stem. My Fr8 bike, which has incredibly beefy tubing everywhere else, has a quill stem that can accommodate the Yepp Mini and the Bobike Mini. Have you looked at all at Bikes Direct bikes? I have their Windsor Kensington 8 and really like it. The Dawes Eclipse looks like it might work for you:
http://www.bikesdirect.com/products/...pse-city-bikes