Rockshox 600psi shock pump. Has done the job for me so far with a Monarch.
Not sure how but when I bought a 300psi pump from Amazon, it offered me a deal where I could get the 600psi pump for £4 as an add on item.
I keep the 300psi in the kit I carry about and 600 at home. The 300 is plenty though. My Monarch seems to only need about 150psi.
The Reverb on the other hand I find the 600 is more accurate and easier when getting it to 250psi.
p.s. you aren’t losing air on disconnecting, or not much. You hear an escape from the pump, but you will lose some on reconnecting which is why it measures lower.