I made the transition to a SAHM a little over a year ago (well, actually I still work from home but that's a different story). I think the biggest thing that helped me to keep "in check" was that this is just like any other job, albeit the most important job you'll ever do, and like any job you'll have good days and bad days. Days where you love what you do and love your bosses (the kids! lol!), and days where you want to lock yourself in the bathroom and never come out again. But the good days usually far outnumber the bad days, and you'll have those no matter where you go anyway.
I'm still working on this part myself, but my goal for this year is to let go of the things I feel like should be done since I'm home, and focus more on my kids. That's why I started staying home in the first place, right!? Not to cook and clean all day!
Lots of mamas mentioned on here getting out at some point for the day. That is super helpful! But also, cut yourself slack on the bad days where you never make it out of pjs, still haven't showered, and the house is a disaster. Oh well, tomorrow will be better! And lastly, take everything with a grain of salt. Kids can be EXHAUSTING. So do the best you can and leave the rest to God.
Best wishes to you as you embark on this awesome journey of being a SAHM! There is nothing better!