If being a SAHP is 'doing what WOHP do, but with more time', why don't Nursery Workers have sidelines, during working hours, or second jobs, or Teaching Assistants?
If the OP goes back when the Baby is 12 months old and mobile, the work is constant. It's a matter of luck if you have an easy baby, or one that sleeps.
OP being a full time Parent to an under 5 year old, is a perfectly valid role and situation. Like most Female roles in our Society, they are looked down upon and undervalued.
We should be supportive of Parents who opt for this. It doesn't make sense that my age group, 50+, struggle to get work, yet we are overstretched during our child rearing time.
Also with the rise in population, we need people to be happy to not be in paid employment.
You don't need to make a decision now. Just tell people that you'll do what suits you, when the time comes.
You might change your mind, or your DH might, so it's not worth arguing about.