Yes, I believe a buck-only option would now be most suitable. Our business is rather new to the electronics market, this would only be our second commercial venture.
We shall be looking to comply with BS EN 60601-1-2:2015; which we've successfully navigated in the past.
The pump manufacturer has highlighted that the specific series of pumps we intend to use (not in my hand yet) are rated at just 35W, so just 1.5A if this helps with any further suggestions.
To meet the demands of the pump before the batteries internal cut-off is activated, we would need to see a duty cycle >98%. I'm certainly happy to handle a few parts to find one that works.