Can you get something to turn a lap belt into a 3 point seat belt in a car?

Title says it all really. Basically, I am about to have another baby, meaning we will have a newborn car seat, a toddler car seat and a booster seat in back of car, the booster seat will have to go in the middle cause don't trust my toddler next to new baby but also I'm not happy about having my 3 year old in middle with just a lap belt on but can't afford a new car, is there anything I can buy to make lap belt into a 3 point belt?

Thanks