Another thing worth considering is a private room at a hostel.
Agreed, I went there last May and stayed at Richterswil youth hostel. I got a private room for £162 for three nights - no en-suite facilities, not even a washbasin, but it had a writing desk and a lockable wardrobe.
Richterswil youth hostel is right by the station, next to the platform where you arrive when you are coming from Zurich. It's about a 30-minute journey by S-Bahn from Zurich main station, and it's right on the shore of Lake Zurich.
There is also a youth hostel in Zurich city centre. Go to the Hostelling International page on the YHA website at
https://www.yha.org.uk/places-to-stay/hostelling-international and select Switzerland and Zurich, and it will come up with both the Zurich and the Richterswil hostel.
In terms of eating establishments in Zurich, the "Bona Dea" vegetarian restaurant in Zurich main station is worth a mention - even if you're not vegetarian or vegan but are happy to try vegetarian food. They do a self service buffet for CHF 29 for one plate full of food. You can even book a table via their website (which only appears to be in German). See
www.bona-dea.ch