I have a similar bilge situation as you, diaphram pumps as well. I have a bulkhead to the underside of the sole, separating the under-engine area. My solution. A 1" square batten with flat "L" shaped brackets at top and near lowest point. drilled holes thru which a 3/8" tube slides vertically. At the bottom of the tube is a standard toilet type float, which when rising, activates a standard rule
switch mounted at the top of the batten. The switch is always dry, and can be easily tested from the engine
bay. Has worked well for years. Photos on one of my older posts, maybe 3 yrs back. Not a fan of big main bilge pumps being submerged deep down under the very stuff that is trying to drown you.