Beesbalm hates me. Same with lavender. I've tried numerous times to grow it including buying healthy starts. It always goes toes up and dies but every year I buy it to try again....I'm not doing yarrow, but I'm doing beesbalm, salvia, and milkweed from seed. Some indoors, the remainder I plan on just scattering when it's warm. I bet you could do the same to see how they fare. I'm doing about 8 of each variant in soil blocks and the salvia is already an inch high. I expect yarrow is pretty similar to those in regards to growing. I will say the beesbalm is very slow growing inside. It might fare better when I throw the seeds in the beds in May.

I've started a flat (Group 1 of 3)of some cool weather flowers indoors - marshmallow, lavender (a different variety than the English), Penstemon, Clarkia, Violas, and Stocks.
Group 2 of 3 for flower starts wont be for a couple of weeks but will include the yarrow seeds I bought. I will likely do what you mentioned and start some in flats and some outside direct sowed.