I have two Thurlby 'Digital Storage Adpators' DSA524, one of which would do what you want to do as well as considerably more (including dual beam, if you can see them on a screen that small
). They're also quite small if space is an issue and you want to keep your existing scope. More about them in this thread, and a user manual at post #6
https://www.vintage-radio.net/forum/...d.php?t=142128
I see you're in Manchester - I'm in Whalley Range. PM me if you'd like to bring your scope over and try one out. If it was any use to you, it would be cheap.
cheers
Mark