These CH breakers should be compatible with SquareD Homeline (HOM) breakers (make sure they say HOM and not QO). Eaton breakers would work too, but i'm not sure they have as many tandom options as square d.

I can't tell if your panel is compatible with tandems yet though. Can you show me the picture diagram that should be right next to all this? it'll have a bunch of squiggly lines beneath a main breaker. slots that have 2 squiggly lines instead of 1 are compatible with tandems.

Sometimes it'll tell you how many breaker slots there are and if it says 20/30 slots then 10 bottom slots can be tandem, or 20/40 means all slots can be tandem.