I don't know the soil conditions in your area, so I don't know if you need a DD coil. You will at some time need a smaller coil. You said you had older homes to hunt. I usually don't need the smallest coils to hunt these because for me they aren't that trashy. As Bob said the 5.3 and 4x6 are your choices in Whites coils. Parks, concession stands, bleachers, and sidelines are where these coils are needed to get in between the bottle caps, tabs and screw caps.
Everyone's hunting is different. For me most of the time I get away with a 10" and 6" coil. Both of these are DD coils. Remember, this is for my soil conditions. Rob