@EmmaS I agree with you it would be great if Monzo offered a credit card. Unfortunately they have never given the impression it is in their plans.
What Monzo are testing at the moment (starting with Barclaycard) is providing the ability to view your 3rd party credit card balance within the Monzo app. I would hope this would eventually develop to allow you to view and track your credit card transactions within the Monzo app.
I’m curious why you use HSBC credit card as a travel credit card? HSBC cards don’t appear to have particularly good features for travel. The cards mentioned already in this thread would be good for travel due to absence of currency conversion fees, but they’re not out yet. In case you’re not aware of MSE, some recomendations for currently available travel credit cards can be seen here. Barclaycard may be a good bet if the idea of having a good travel credit card that might be viewable in the Monzo app in the coming months appeals to you.