Different machines take different needle sizes, size being defined as total length of the needle, distance from the non-point end of the needle to the eye, shank with a flat side, completely round shank. Over time many machines adopted the Singer standard for domestic machines, that being 15x1. The 206x13 needle, for example, was used by Singer in its 306 machine, as well as a few others.
Boye was an aftermarket distributor of needles, shuttles, and spindle bobbins. Boye items typically came in a round metal dispenser or a wooden cabinet. Boye had its own numbering system. For example, a 15x1, the Singer standard, is equivalent to a Boye #16 (older Boye dispensers have a different numbering system; I am referring to the "newer" Boye dispensers.
Your machine takes a CC1221, the Boye equivalent for this was a # 2 1/2, and I think Kenmore's equivalent was a No 49, but all the same size needle. This is why I suggested looking for Boye 2 1/2, along with CC1221, they're the same needle.
Within a specific size of a needle (as described above) you can also find different (sub)sizes (my terminology) which refers to the thickness, or heaviness of a needle. There are old and new designations. For example, if you were sewing denim you might want a size 16, a heavier needle, versus say a size 11 for sewing very lightweight fabric. The heavier needle is sturdier for heavier material, a lighter needle makes a smaller hole as well. I think the new designations for these sub sizes are multiples of 10: 80, 90, etc.
To make matters even more confusing, needles also have different style points, for how it pierces the fabric, chisel, ball point, etc. This is a factor also depending on the material in your work. You can look these up easily enough.
I hope this helps.