The best way to do this ime is with squats and deadlifts, with the heaviest weights you can handle safely
Came on to say exactly the same.
I've been running and playing a team sport for years. But I've not experienced such rapid improvement in my arse/legs/hips as when I started deadlifting/split squats. The change was quick and very satisfying.
However, your weights are too light for a really effective deadlift workout - at your height/weight/fitness (roughly similar to me when I started), you could probably lift over 30kg as as starting weight and expect very quick progression. Six months on, I'm closer to 70kg now (pushing for 140% of my body weight - 150% next target!).
So split squats is more reasonable for the weights you have - even body weight here is a decent start. One leg up behind you on the stairs or a bench, the other planted in squat position. Slowly lower your arse to the ground, hips level, core braced, until your front thigh is parallel to ground (make sure your knee doesn't move ahead of your foot), pause, then explosive movement up. Repeat for 10 either side. If it's easy with body weight, start carrying weights. For reference, assuming similar body shape/fitness again, I am up to 30 kg on each leg (I have to wear a weights vest because I can't carry 30 kg on my arms
)
And agree with Barbara - if you're not struggling to get your 12th rep out, it's too easy. I move up a weight set when I can do 12 and still have another rep left.
See picture for split squats (although I do them with my back leg lower than that):