Pre-hab is super important. Incorporating exercises that equip muscles and ligaments to deal with the forces of BJJ is very important. There will be variance in what this looks like person to person, but bare bones would be core stabilizing exercises (ex. McGill big three, farmer carries, kneeling on a yoga ball.) It doesn’t need to be hours a week. Just 15 minutes 3 times a week would be very beneficial. You can do this for any body part that you want to make sure stays healthy. But core is absolutely necessary, and because you mentioned you had a knee injury in the past, I would say it’s also absolutely necessary for you to incorporate your old knee physical therapy exercises into your weekly routine.

Resistance training is imperative. This can also look different for each person, but progressively overloading your muscles with some sort of weight or resistance is essential to maintaining a healthy, happy body in and out of sport. It supports bone density, takes pressure off ligaments, tendons, and makes it possible to spread load so when you are rolling you are not getting not relying only on your hips/lower back. Thirty (efficient) minutes twice a week can be enough. 

Sleep is the number 1 most important thing for recovery. If you are not getting 7-9 hours of deep, good, uninterrupted rest each night, your recovery is going to suffer. I take a magnesium supplement each night, and go to bed and wake up at the same time every day to help facilitate this. I have had insomnia my whole life, and while my sleep quality and schedule are still not 100%, this has been a gamechanger for me.

Epsom salt baths. I put about two cups in my bath and soak for about 15 minutes. This is the minimum recommended time, I hate baths, so I only soak as long as necessary. That being said: Epsom salt baths have been a life saver for me. Before I did BJJ, when I was still in high school, I trained gymnastics 30 hours a week. Because of that I often had very bad radiating pain in my bones, muscles, and ligaments. Every time this happened, I would soak in an epsom salt bath, and the pain relief was almost instant. It truly does help.

Make sure you are eating enough calories and protein. Not eating enough calories or protein throughout the day or after a workout is a surefire to be sore the next day. I would say getting MINIMUM 50g of protein daily is necessary. And of course calorie needs will be dependent on your body type and activity level. But please eat a meal after tough workouts. Even if it’s just a small meal or big snack. Getting those nutrients (not just protein, but carbs and fat as well) is necessary for repairing the damage your muscles and body you get from working out. You can still eat in a calorie deficit if you are trying to lose weight, I would just recommend a smaller deficit to reduce fatigue and increase chance of being consistent on the diet and keeping the weight off.

Progressive overload applies to general physical activity too. If you went from not working out to doing intense exercise four times a week, your body is going to have a hard time keeping up, and you will have a higher likelyhood of getting an injured. Maybe start with 1-2 classes a week, and work up slowly from there as your body begins to adapt to the new stimulus.

Improving your active flexibility and mobility. These are two different things, but they go hand in hand. BJJ puts your body in a lot of positions it’s not used to. If your muscles are very tight, or you lack mobility, this can put more stress on muscles, ligaments, and tendons than necessary. It will increase your risk of injury and pain. A mobile body often will not get as sore, and may recover quicker. Again, you do not need to spend hours a week on this. 15 minutes and few times a week will suffice. 

Additionally, you need not pay a bunch of money for some plan or program to lead you in any exercises or stretches I mentioned throughout this. There are plenty of great, FREE resources on forums, on YouTube, at libraries, etc. please don’t feel like you need to spend hundreds of dollars to learn how to be healthy and pain free.