My go-to workout is a park workout with dips, push-ups, pull-ups, box jumps, bur-pees, sprints, medicine ball and ropes. But my strategy is to stay lean, flexible and have monster cardio. I lose plenty of rolls, but I never lose because I'm tired/gassed. Other guys I know do Olympic lifting and rely on pressure, control and power passing.
But it depends on the type of workout you like, the type of BJJ game you're building, etc There's good free stuff on YouTube, and also good $ stuff on BJJFanatics.com.
I realize you didn't ask about technique......but just wanted to comment. The issues you're experiencing (thrown out of side control, slammed on sweeps, etc.) are fixable in a lot of cases with adjustments to your position, posture and movement/reaction to the reversals. Ask your coach/instructor if he or she is seeing anything that you can adjust, tweak, etc. in your game. It could be something you can fix in just a few sessions of training. Also, when you get reversed, smashed, etc. don't be afraid to ask your training partner what they are seeing, how they're doing it, etc.
I will admit that there are monsters on the mats that are huge, and strength/size can be a pain to deal with when the disparity is big. But the reason an advanced belt can easily control a big/strong lower belt is almost all about technique. Hope that helps...not trying to derail your original question. Just trying to help share some experience.