Re: stairs down to the stalls - in future, then, avoid the Savoy and the Criterion. In both those theatres, you have to take stairs down from the entrance to the *upper circle*. And then more stairs down to the dress circle and the stalls.
(The Criterion is built on three basement levels. The Savoy is not below ground but the building is built on a slope down from the Strand to the Embankment, and the entrance is at the Strand level and all three tiers of seating are on lower levels.)
The seats in the Ambassadors are notoriously uncomfortable. The circle is possibly worse than the stalls.