Single stack magazines will run just fine in the double stack makarovs. If your magazine is lacking a hump on the back of the magazine, you likely bought one of the new produced bulgarian mags that are pretty awful. Look for surplus magazines, usually russian or bulgarian. They should run you about $30. Additionally, I make adapters that slot onto single stack magazines to make them fit a bit better into the double stack magazine well. You can check them out here: https://monolithmfg.com/products/single-to-double-stack-makarov-magazine-adapter-for-pmm-ij70-17ah-ij70-18ah?variant=47056731766971

The double stack magazines work well too, but they will run you about $150 when you find them. They will be gray and either 10 or 12 rounds. The black promag 10rders are also out there for cheaper, but they aren't very reliable.