You don't need exercise variety - you just need to make the exercise harder
So to be clear exercise variety is great., and if variety helps you stick to a workout routine then even better. But you can get stronger and fitter doing the exact same exercises - you just need to make them harder.
What is progressive overload?
In order to get stronger, you need to increase your training stimulus (i.e, how hard you're working) over time. So, for example if you did 10 bodyweight squats every day you may initially get stronger than you were before starting this routine. But unless you made those squats harder over time you wouldn't continue getting stronger. In other words, your strength would plateau
So how do you create progressive overload or 'make things harder'
You need to train with an intensity slightly above what your body is typically used to. You can do this by:
Add some weight
If you don't have any weights at home just grab a few cans from the pantry or fill up a couple of water bottles. You can always start by adding weight for just a couple of repetitions, and then drop the weight for the remainder of your set
Add an additional set.
You might not be able to do as many repetitions in this set as you did in the few prior and that's okay, just gradually build up to it.
You can slow the tempo down of the entire exercise or add a hold or a pulse at the end of each repetition
Try and finish the same number of repetitions in less time. Or take a shorter rest time between sets.
Go for a single leg or single side option if it's available.
Increase your range of motion
Squat or lunge a little deeper. Push a little further into your back bend... you get the idea.
Or use a combination of the above
Just remember if you're new to training or returning to training after a break you need to gradually build up your training intensity.