Hello Octavia,
The dress code on the
theme park FAQ page states, in part:
"Attire that is not appropriate for the parks—and which may result in refusal of admittance—includes but is not limited to: Adult costumes or clothing that can be viewed as representative of an actual Disney character." Masks are also not allowed.
Most interpretations of this I've seen indicate that it's fine for adults to wear a small part of costume or something that suggests a character, but not something that would let you be mistaken for a full-on actual Disney character. For example, it's fine to wear your hair in a bun with a tiara, but not if you're also wearing a blue ball gown.
If your hoodie and matching pants are clearly a hoodie and pants, then you're probably OK, if they overall look like a costume, then maybe not. Something like a Cheshire Cat hoodie with jeans would very likely be permitted. The final say goes to the the cast members at the park.
Good luck with your planning. Please let us know what else we can do to help.