Selection of pneumatic control valve with pressure activated positioning

I am building a device to help my wife who needs constant massage to prevent her condition getting worse.

Would love some advice on selection of a valve :
I need a low pressure, high flow control valve for my application (light weight would be a nice to have also).
The flow control is 2-position 2-way, the position control should be by pressure pilot (from high pressure side line).

The circuit : See image
I have 2 tube accumulators that need to be alternately pressurized in a constant cycle,
switching once each sides PRV reaches the threshold pressure which will activate the control valve
and shuttle it to the opposite position (effectively using PRV's to alternate the pressure side of the circuit.)
Additionally I want to pump water, but as air may mix in the lines I'm making it pneumatic fittings for leak purposes - plus it's low pressure, less than 0.25MPa.

Can anyone make a recommendation of a model/manufacturer please.
It's only 4-6 units that I need initially.
I thought it would be easy, but can't find one that is pressure positioned in any search so far.

I am self-educating as I go, so I apologize if the terms are not correct.
Thanks and Regards Matt

Circuit - dual Accumulators.jpg
Extra info/specs:
Water Pump 0.5MPa max. pressure (likely a positive displacement type)
Low pressure and Low flow (Not High Flow as stated in first post)
Flow rate 0.2 litre/sec - 5/16" | 8mm line and fittings size should be fine for fluid transfer + losses.
Accumulators are in a vertical arrangement , so gravity will assist with the de-pressurization (filling of the reservoir)
hey Matt
I would give Festo or SMC a call they are specialists in valves...I would imagine you need some control element to your design I doubt that it would work as you've described in your drawing without some electronic controlling device.
You could also do away with the hydraulic/pneumatic and go electrical/plc/motor/sensor/peristaltic pump....which might make some sense if you're doing development work.,,,,,rewriting code is cheaper than buying new hardware on a mistake