Sub maximal singles can be performed often too. I do gradually ascending singles in the squat until I hit my working set weight and do 6 singles with it. My working singles being around 90% of my 1RM. This is how I train squats for probably 95% of the time and it works great, and since I only do 6 singles, it doesn't tax me much because the actual volume of working weight sets is low.
You might try 5,4,3,2,1 too. The way I do it is to figure my 1RM, and figure that the final 1 rep of those 5 sets will be about 95% of the 1RM. 4th set is 90%, 3rd set is 85%, 2nd set is 80%, and the 1st set is 75%. This will get you lifting very close to your max, but not quite. Great for 3-4 weeks stints, but it's a little too high on the intensity to do for longer periods than that. I'd probably drop down to 75% the week after my last week of 5,4,3,2,1, and then resume my regular lifitng schedule the next at 85-90%. This is just how I do it. There are so many different methods.