106-111: The trill starts on as a 2-3, then continues as a 1-2. On 111, it's 3-5.
338-342: The trill is 2-3. On 343, it's 1-2. The octave strikes can be played alone on the attack, the trill can follow. Meaning, you don't need to ever play 3 notes at once (B flat + octave.) This is especially important on the G's (mm.339, 341,) and the B-flat octave in m.340. Immediately after the strike, I jump down to a 2-3 trill. It's ok if there are gaps in the melody; and, this passage doesn't need a lot of pedal to sing, because those high notes do not have dampers, therefore holding them with your 5th finger is a waste of tension. A fast strike makes them bell-like, and a perfectly delightful closing theme at that.
366-371: A very tricky passage, mostly to keep the dynamic down, for the cresc. to be meaningful. I keep the trills at 2-1 all the way through. RH is 2-1, not 1-2, even in 368. It's ok to abandon the trill right on the downbeat to leap up to the B-flat in the melody. This 2-5 stretch is musical, because it gives the melody that bell-like quality, by being picked at from below - a kind of earth and sky effect. You are not 'cheating' by not holding onto the melody - on the contrary, I think the texture affords it - and you can use pedal. After all, this is the measure with the cresc.
As for the LH - also difficult. I keep it 2-1 all the way. If you LH is sluggish and tight in the 3-4-5 range like mine, it is very difficult to be melodic here. It's subtle, but I avoid ever playing two notes at once. Every strike of the moving line is alone (not counting the top line - of course, they are struck together.). In this cloudy texture, and with the speed of the trill, it can be seem seamless. A lot of what goes on on a piano is an illusion.
372: The downbeat is 2-5, but then I immediately switch to a 1-3 trill. I abandon the B-flat in the RH, and keep the pedal down. This is the one and only cadential trill, and it is beautiful when mixed with pedal.
I get so much out of this sonata. Do share any thoughts you have.