Convert from 60 to 30 FPS with slow motion, but also scale effects (keyframes) to new timeline

Hi there

I'm not totally sure what terminology I should be using here so apologies for that, but I have a project with a sequence that matches the source clip's framerate (60 FPS), that I've already applied effects to including some quite complex animation using multiple keyframes (200+ keyframes!)

I've now decided I'd like to slow this whole thing down, taking advantage of the 60 FPS recording and converting it to 30 FPS slow motion. Normally I'd do that by re-interpreting the clip to 30 FPS before creating a 30 FPS sequence, but if I do that I'll lose all the work I've already done on the 60 FPS sequence.

Any ideas? In principal it seems like it should be simple enough for Premiere to just adjust the keyframes to apply to a longer timeline, but I've no idea if this functionality exists. Perhaps the only way is to export this as a 60 FPS lossless file, then create a new sequence from that clip just to slow it down to 30 FPS? What about a proxy export? I've never proxied anything so don't have a clue.

Thanks!