Help: Crawlspace encapsulation or Vapor Barrier+Fans? Serious air quality issues in house.

We've been struggling with air quality issues in our 1,800 sq. ft. one-story home (built in 1913) in Los Angeles ever since we bought it two years ago. Symptoms like tight throat/chest, headaches, and difficulty breathing make living here extremely uncomfortable. After much research/investigation, we believe the crawlspace is the culprit due to the stack effect.

Our crawlspace has consistently high humidity (60-80%), which is abnormal for LA. We've consulted several companies, but the recommended solutions vary widely.

We’d greatly appreciate your input on the best approach:

Option 1: Vapor barrier + vented crawlspace (quoted by 2 companies ~$7,000)

• Install a 12mil vapor barrier covering the crawlspace dirt
• Air seal floorboards/joists to reduce air transfer
• Install R19 fiberglass batts between floor joists
• Install vent fans for crawlspace ventilation

Option 2: Full Encapsulation (quoted by 1 company ~$19,000)

• Fully seal the crawlspace and basement (close all vents)
• Install a vapor barrier on both the crawlspace dirt and basement floor/walls (Cleanspace)
• Add drainage mat under the vapor barrier (excluding walls)
• Install a dehumidifier with a condensation pump
• Sump Pump install under vapor barrier
• NO under-floor insulation, as it's believed to trap moisture

Given our urgent need for a solution, which approach would you recommend? We’re at a loss and would truly appreciate any and all advice. Thank you!