I would try and avoid smith machine squats for the time being. They take away a lot of the supporting strength from traditional barbell squats, and lock you into a very linear movement (i.e. up and down).
I'd also avoid the leg press as your main lower body movement, as it doesn't involve the spinal erectors as traditional squats do.
Instead, you could consider:
- Goblet squats
- Bulgarian split squats
- Pistol squats
- Overhead squats
- Step ups
- Front squats from a clean
- All of the above
A few years back Mike Boyle famously (infamously?) stopped his athletes squatting and instead concentrated on Bulgarian split squats (aka rear foot elevated split squats).
Dan John has written extensively about the benefits of goblet squats, if you think they're easy, grab a 50kg dumbbell and knock out a few sets of 20 reps.
Lunges, although occasionally given a bad rap as something 80's lycra clad aerobics class attendees would do, are an amazing strengthening exercise. Again, if you think they're easy, grab a couple of 30kg dumbbells and do walking lunges the length of your gym. Then turn round and do the same back.
Pistol squats, overhead squats and step ups I'd put more as accessory work / assistance lifts, but they're still very useful and valid squat alternatives (pistols can be difficult to load, overhead squats can be quite technically complex and step ups require something sturdy to step up onto).
Front squats from a clean (because you don't have a squat rack) are a possibility, but there is a significant learning curve to the clean movement, meaning that other options may be better for basic strength training.