We really enjoyed staying in the attic of the Heidel-home. The kitchen had everything we needed to cook for ourselves (saving us a lot of money), the bed was comfortable, and the heaters worked wonderfully. All our interactions with the owners were excellent, and they were gracious to us after we had to cancel our initial booking due to passport issues and offered us a discount the second time around. (We couldn't get a refund since we had booked through a third party, but that wasn't their fault.)
The apartment itself is close to a couple grocers, and the walk to the old city center is not bad. You can also take a bus since it's only one straight line to the Bismarkplatz right outside of the old town. It is also close to a local train stop and within walking distance of the main train station.
Our only warning to future guests is maybe if you are tall you should go for one of the lower floors! We are fairly short people and we still kept running into the sloped ceiling.