Thank you all for your advice and anecdotes! It's been very reassuring!

By a momentous stroke of convenience, there was a pushchair store that's open on a Sunday, literally across the street from where we're staying. Their least expensive option was a 245 EUR Cybex (which delightfully is also the kind that will fold up as a carry-on), or about 35% of the original bundle price of the M&P pushchair that BA lost.

I'll submit the claim once my credit card deigns to display the figure in sterling. Thanks again!