best way to book multi-city europe trip?

hi everyone. i’m trying to book a trip to london and copenhagen, and wanted to know the best way to go about this. we want to stay in london for a week to visit family, and then spend 3 days in copenhagen. should i use google flights multi city? book through ryan air for the flight to cph?

my mom used to plan our family trips, but unfortunately she passed away, and now i’m left to do it. i’m honestly pretty nervous and afraid of messing something up so would appreciate any help lol