Boy, are you playing my song! I, too, was a single mother with a hefty mortgage. So, I found amazing ways to save money. I can't go into them all here; but, a few of them are:
1. Check your local dollar store before you go grocery shopping or shopping for anything for that matter. Many dollar stores get products from stores that are going out of business and sell them cheaply. One of my examples is the cat food I picked up last night at the dollar store. Usually one can is approx. $1.50 in the grocery store. I got 4 cans for $2.00. Good deals like that everywhere.
2. Buy in bulk. My kids and I enjoy rice; so, I bought my rice in 50 lb. bags. Cost so little and lasted so long. During growing season, I would go to the farmers' land to buy my produce - 50 lb. of potatoes for $10 is a deal I can't pass up.
3. Don't be afraid to buy extra of things at a killer price especially if the product is freezable.
4. Go to thrift stores for clothing (except underwear and socks). There are many excellent outfits available at a thrift store for a fraction of the store price.
5. Look to your community center for inexpensive things to do with your children. They have all kinds of courses; arts and crafts; physical activities; lessons; etc. for very little or no money. My daughters loved to swim; so, we went to the FREE swim at the pool at least once a week. Great, wholesome physical activity that had all three of us engaged with each other - all for free.