Hi Alternety,
Interesting situation.
I presume that there was not an existing method for determining well
level ... ?
If you have considered various other methods, and you have decided that
the 'bubbler' technique suits you best, then i suggest using a pump
from an old kitchen refridgerator.
Or from an old shop freezer unit, or some commercial cooler display
cabinet.
They run happily in the pressure range that you mentioned, and they are
designed for very long service life, and to run reasonably quietly.
Such a small 'motor-compressor' would be overkill for a small domestic
well, but for what you describe it might fit the bill. The volume of
delivery from these type of pumps is quite low, but you may have to
throttle it back further, to suit yourself.
Another possibility is that you may not need continuous indication of
the water level.
If your well takes a long time to fill before being pumped out, then
maybe a bicycle pump would do the job, perhaps each day?
Or maybe morning and night ?
Every hour would be too often to pump up with a bicycle pump, but it
might be Ok to do it with a small fridge-pump.
Don't forget to allow the reading to settle, there might be a lot of
water to push through the sensor pipe before taking the reading.
Best of luck with it, John