SW is just a way of restricting calories, it's not a magic spell that has to be followed to the letter to work
. So you can go off plan a bit and if you do it sensibly it won't affect your weight loss. The main way that SW works is by restricting you to tiny amounts of obvious junk like sugary/fatty/processed crap.
There are a lot of overlaps with low carb, but obviously the main difference is that you shouldn't be doing high fat. But then if you prefer to do LCHF, why not just do that instead?
But if you want to follow SW SP and low carb, you could have nuts as your B choices. A tablespoon of olive oil used to be a B choice, but isn't any more, so you could have that - it used to work fine, so still will.
You can also have lots of eggs and 5% fat mince so some fat there. You could have loads of veg and salad and little or no fruit. I find that unless you are having loads and loads and loads, it's fine to have plain full fat cottage cheese, Greek yogurt etc and 2/3 HEAs a day.
You could also substitute some of your B choices if you don't want bread and cereal. Each one is equivalent to 120 calories, so just have that amount of something else that fits into the low carb way of eating (avocado, cheese, butter, whatever). If you are eating lots of veg and salad, you will be getting enough fibre anyway.