After a year of simple fit I started mixing things up as well by throwing in some weight training, although not the typical weight training that I used to do when I was a gym rat. I do a day of simple fit, then a day of a crossfit workout that includes an olympic lift, like a thruster workout or snatches, then another day of simple fit then repeat. This is what worked for me.
I'd take it slow with olympic lifts at first if you've never done them before and maybe do 2 days of simple fit to 1 of lifting. Make sure your form is good and don't sacrifice form for weight.