I do not want to fall back into re-observation.
Note this and the sensations involved too, not doing so may be part of what's holding you back.
My question is how I can optimize my practice to get stream entry as soon as possible?
Bring noting into your daily life from the moment you open your eyes in the morning. This is all about momentum and getting to 'escape velocity' so note accurately whenever the opportunity presents itself, this will also help by allowing you to examine sensations which may not occur during a sitting.
Is there perhaps some way I can organize a 'solo retreat'? I just want time and space to meditate all day every day for a week or so.
If you've got the time to do so, I highly recommend it. I only even did one solo retreat but it was incredibly useful.
today's meditation was remarkably broad and effortless, it seems like my main barrier is the watcher/watched duality.
Excellent. Equanimity is more about paying attention than noting ferociously, concentration is high at this point so use it and watch how each sensation, the pleasant, the unpleasant and the neutral ones, just appears, does it's thing and vanishes. You've already seen this in the A&P but it was really fast, this is much more fluid and natural, but in the laid back equanimity of this stage it's easy to wander off or put all your emphasis on one sensation, then catch yourself doing it only to find that you've lost your focus. This is about inclusiveness, see every sensation as being the same, and that includes that sense of there being a watcher to be doing the watching. Look at the sensations that make this up and how they arise and pass, just like everything else.....
Good luck, let us know how you get on.