Hi there JIsandi. Welcome here

From what you've said it seems that you easily meet the Financial Requirement as a Category A applicant.
Is there a specific reason why you believe Category B is your best approach ?

.....just get a letter from my landlord confirming that the current tenancy will renew for a min of 6 months when my spouse arrives?..
That's fine.

Under the specific circumstances of your accommodation as a house under multiple occupanacy, I would suggest that you submit an independant report clearly stating that the accommodation is both adequate and is not overcrowded.
This application is too serious to take a risks at all.
Houses with multiple occupancy, not family owned and resided in do often fall for refusal. Better to be safe.