Something green to replace the impractical malachite. I would looove jade. Green jade especially. But lavender jade is nice too. Also green agate, or chrysoprase. Maybe green mother of pearl?
I think a quartz variety would be nice too. Like amethyst, citrine, or prasiolite. But since the holiday pendant has the metal on the other side for engraving, I’m guessing it wouldn’t be a translucent stone.
I would also love aquaprase, which I learned about from Boucheron. It’s a blue-green variety of chalcedony that was recently discovered. Everything turquoise colored reminds me of Tiffany, so yes, I would obviously love that. (Attached a photo, because it’s so stunning.)