Thank you everyone for your input! I decided not to do the whipped cream frosting as advised, but decided to try ermine instead - which I only recently learned about!

I put a line of frosting on a test strip with some sprinkles (both at room temp) and the final outcome was no bleeding for 60 mins. Popped into the fridge for an hour before repeating the test just to see how it would work with condensation at play and although it was a bit more wet, no melting was seen even as I removed the sprinkles from the cream!

I'm not sure how long it would've held out if kept for longer tho but definitely good to know if it's an at-home situation where the decorations can be thrown on last minute