Thanks jimmyt - that Hotel Locanda al Leon sounds OK, and I'm checking it out.

A classic example here, though, of the way reviews sometimes seem to reflect something other than the actual quality of what's being reviewed.

Most of the people who commented clearly loved the place - here's one, a New Zealander:
This lovely hotel was exactly as described on the internet. Great location,around the corner from San Marco, but the sound proof rooms offer a welcome respite. Rooms were clean, minibar prices the cheapest we encountered in Europe and the breakfast excellent. The hosts were friendly and welcoming. Definitely recommend this little gem.

But here's what another (from Miami)had to say:
The people writing these reviews must be on acid. Arrived in Venice in a rain storm was walked over to Cavenella and almost fainted - a total dive, dirty and depressing. Asked for a refund because property was not like what is shown at various sites. Got back to the states and this sleeze ball put in 3 extra credit card numbers. The owner must have many family members writing reviews because this place is best rated as a dive.

I think I'd trust New Zealand (and jimmyt) over Miami this time round...