Perlite for transplants

[angelique]

I am a little confused. Once my seeds have their first true leaves should I upsize them to larger pots (4x4") filled with a seed starting mix?

I ask because a couple of my tomato plants have their first set of leaves (Latah and New Big DWARF). I started them in seed starting mix from a local nursery. I have a large bag of perlite (1/2 a 4 cu ft bag). I want to know if it would be possible to fill the 4" sq pots with the perlite, then relocate the seedlings with the original starting mix into the perlite filled pots.

Any advice either way would be great. I want to make sure that I do what is best for the transplants.

Thanks.

Angelique