EpicAdventure, you also can mount transom platform on many boats. It wont be a walk-through, but, for healthy dog, it should be enough to jump in and out
Sailboat Transom Platforms - Custom Marine Products
About boat choice? I would take Freedom 38. I own smaller Freedom, and I don't see why people sail other brands
You, as a scow sailor, will enjoy every second of sailing Freedom - dingy-like simplicity with nice interior.