Do not squat alone unless you have a squat rack/cage with safety bars in place.
Don't do smith machine squats.
If you don't have a squat cage/rack, you can't squat with just a barbell because if you had enough weight on the bar to do squats, you wouldn't be able to get it up on your shoulders.
So here are your options:
Deadlifts - they work your quads a bit (not nearly as much as squats), and they'll also make your lower back and grip strong as hell.
Lunges with Dumbells - they can work your quads really well
Bodyweight stuff such as pistols (one legged bodyweight squats) - probably the bodyweight exercise that hits your quads the most. Mix these with Hindu squats and jumping Hindu squats if you want to change things up.
My best advice would be to join a better gym that has squat racks and/or squat cages.
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