Fiberglass batts have been a great solution for decades
High density batts r-15 provide a longer lasting solution
Blow in Blanket systems are a
Some of the crawlspace work we offer
Replace or install a 6 mil vapor barrier (moisture control) encapsulation to keep floor joists and wood floors dry. Homes older than 20 years may not have vapor barrier and insulation as it was not required building codes back then.
To the vapor barrier encapsulation add drainage with a sump pump in lowest region and plumbed to outside.
To the vapor barrier encapsulation and drainage add dehumidifier plumbed into a pump that removes the water. This will ensure that your crawlspace remains dry.