Get what is called a "squat cage" (you can build one yourself if you don't like the options to purchase.) along with an Olympic bar (it is a bar weighted to 45 lbs. along with Olympic weights.
You can do squats safely without a spotter by using a squat cage. Also, when you place a bench inside of the cage, you can use catch bars to safely bench press without a spotter (the safety bars will catch the bar at chest level when you can't lift it due to exhaustion)
Along with pull ups, bench press, squat, and deadlift are the best exercises for strength. An olympic bar will let you do both deadlift and squat with just a rack.
Just to add that 'safely' in this context means that if you fail at a rep, the cage will catch the bar. Obviously it can't do anything to point out bad form as a spotter, or even a mirror, could.
I use the squat cage at the gym I go to and I wish they had more mirrors. A pair of angled ones so I can see a side-on view would be really helpful.
Don't use mirrors too much. In fact, you should do most of your exercises facing away from any mirrors.
A mirror only shows the front of you. If you stop looking into a mirror, you'll find that your ability to "feel" your form through proprioception becomes significantly stronger. And it will tell you things that you simply cannot view in a mirror. Try doing an entire session without using mirrors; if you find it difficult or impossible to maintain proper form, that should be an extremely compelling sign that the mirror has become a crutch, and not a very good one.
There's also the unfortunate fact that, by looking into a mirror, you're guaranteeing that your head is tilted farther back than it ought to be for exercises like squats. You never want to have your neck extended while carrying a significant load. It should be in a neutral position — for a squat position, this will equate to looking at the floor roughly five or six feet in front of you.
The gym I go to has a mirror running at a diagonal such that I can look front-right of me to see a view of myself half from the side. Not quite optimal for watching my form, but easier to look at without turning my head.
You can do squats safely without a spotter by using a squat cage. Also, when you place a bench inside of the cage, you can use catch bars to safely bench press without a spotter (the safety bars will catch the bar at chest level when you can't lift it due to exhaustion)
Along with pull ups, bench press, squat, and deadlift are the best exercises for strength. An olympic bar will let you do both deadlift and squat with just a rack.