As a single parent, you can claim the eligible dependant credit for your son. It's the new name for the old "equivalent to married" credit. You'll find that in the Dependant's section of your return. You can also claim the Canada Caregiver Amount for him (also in the dependants section).
Until the T2201 has been approved by CRA, you shouldn't claim the disability amount transfer. Once it is approved, you can make adjustments to your return to claim the transfer.
For more info on disability-related credits and benefits, here's a good guide from CRA: https://www.canada.ca/en/revenue-agency/services/tax/individuals/segments/tax-credits-deductions-per...
