Vienna hotel recommendation please?

[space-time]

Vienna Austria. I need a good, reasonably priced hotel for 2 adults and 2 kids. No need for fancy stuff which we will probably not use (pool, spa, gym). I just want to have a clean, safe, nice place to crash at night after roaming the city and shower in the morning. Must have private bathroom. Within walking distance to main tourist attraction would be nice, but we could also take a bus/tram/trolly/subway/whatever they have there if the ride is not more than 15-20 minute.

Thanks (Danke?)

EDIT: this is for late July. does it get hot over there? is AC a must???