I stayed at Motel 1 Sendlinger Tor before and was positively surprised. The rooms are not very big, but had everything I needed.
Motel 1 have several locations across Munich.
Another hotel I stayed at was the Marc, near the main station. However, that is adults only. The hotel was brilliant, but the location is not to everyones taste. When I went there, a wonderful breakfast buffet was included. Staff were very knowledgeable and helpful. I went to see my family at the end of my work trip before staying in Munich for one more night. They stored my suitcase without quibbles when all the lockers at the station were full.
Then I stayed at the Eurostar Book hotel a few years ago. I quite liked it and got a good deal on Lastminute, otherwise it would have been out of my price range.
The Novotel right by the exhibition centre is a typical chain hotel and most rooms are cookie cutter standard. I found the bathroom at this hotel a bit on the small side, but workable for one person. Would be a different kettle of fish for two or even three.
The Mariott in Freising was also great, huge room, great bathroom and restaurant, but a bit far out for a visit to Munich.
I usually go to Munich at least every other year for work, so I have stayed in quite a few hotels.
Travel is currently not really allowed, but if you can get a flexible booking and are willing to stay a bit further out, have a look around the exhibition centre. Quite a few trade shows have been postponed or cancelled so people naturally cancelled their bookings. There might be deals to be had.
There's a Motel 1 and the aforementioned Novotel right by the Messestadt West U-Bahn and right next to a shopping centre (Riemarcaden) with a supermarket, a pub and a few food outlets.