I'm a SAHM. I have a 3yo who starts nursery next week thank fuck
Overall I've absolutely loved being off with her. DH earns enough that it was a choice for me as to whether I wanted to stay off or not.
DH and I both benefited (we feel; different opinions and family set ups all fine!) from having SAHMs and wanted to give it a go.
Luckily my employer gave me a 5 year career break so I do accept I have a massive safety blanket of a job if I wanted to return.
I also luckily made an excellent friend through NCT and we've kept each other sane for these 3 years. I met other women at groups but none I have bonded with like this friend.
My tips would be to fill up your week with activities and classes. The first year I had something on every single day, often a morning and an afternoon event. (I considered a Tuesday pm weigh in as an event, mind...!)
Several things were 'paid for' classes like baby massage, yoga, baby sensory, sing and sign etc, many were groups like a church playgroup for 1.50 or the free library Rhyme Time things.
As she grew older I tried to keep a small routine, we've always had at least one class/event and this has most recently been a forest school type activity.
I echo a PP in having an annual pass for a local attraction. Something with animals is always a winner. They always have café for you and something for the kids.
As they get older I'd say make plenty of plans, hoard rainy day activities like you want to insulate your house out of toilet roll tubes (still don't know what to make with 20 egg boxes and a carrier bag full of loo rolls...) sticker things from the Works, anything you can whip out when you inevitably want to chuck the little darlings out the window...
Also don't be afraid to chuck them in front of the TV just to drink that cuppa. I have totally TV shamed myself a few times but you know what - being a SAHP is pretty bloody hard and it wont kill them to watch Peppa Pig for a bit.
I'm glad I was able to do it and I luckily had an angel for the first 3 years. If she'd had been more spirited I may well have returned to work but that's up to all parents and what their work/child/finances are like.
Good luck to anyone considering it.