I can't recommend Thomas and his place enough. Thomas speaks fluent English and communication with him is super easy. He's also just a very chill, cool guy - something I could see within 2 minutes of meeting/talking to him. He makes you feel welcome and at ease.
The flat is in a wonderful location. I hadn't been to Vienna in 15 years so wasn't at all familiar with its layout, but I think it'd be hard to find a better spot for a week of activities in the city. It's within 20 minutes walk to pretty much all of the major museums and attractions. In fact, I was very surprised halfway through my trip to realize that I didn't even use the metro system or any public transportation at all, except for just one taxi to/from Schronbrunn Palace. The flat is also a 2 minute walk from Naschmarkt, which is a big, outdoor food market with stalls and some really, really good restaurants. I found myself there multiple times since I was too tired to go back out after returning home from a full day of site seeing. There is a middle eastern restaurant in the market called Neni Am Naschmarkt and I highly recommend it. I ate there twice is was so good. The flat is in a very safe part of the city (Vienna is very safe overall) and accessed securely.
Thomas also provides great extras for his guests. He gives you a pocket wifi device that you can take with you anywhere in the city and always have free wife. He has a coffee machine, pod based, that was a GODSEND for me since I need coffee immediately upon waking up. The flat is clean and tidy and everything works properly. The only thing to point out to prospective guests is that the shower is indeed very small. If you're obese/big/wide, it would be hard to fit so just be aware. Overall, highly recommended. Thanks, Thomas!