Laura,
Keep in mind the other thread. Treat your surgical site like a broken bone that needs time to knit. Now that your family is waking up a bit to your real needs, religiously adhere to the no more than 5 lbs. lifted rule until the full six weeks have passed. I did, no matter how inconvenient. It was humbling asking my then 75 year old mother to lift the gallon of milk, but she was easily capable of doing it, and I wasn't. I now can lift both of my children simultaneously (88 lbs. and 45 lbs.) and walk down the stairs carrying them. My chest is fine. It still feels a little odd doing push-ups, but I can do them as well. Give yourself time to heal. Would you try to walk on a broken leg after only 4 weeks of healing?
I would say not.
Stretches and the like are permitted and have much value. I know that in my case I kept on stretching my chest, shoulders, back, etc. until not only did I avoid contractures (where you're always a bit stooped over with a badly curved upper back and a stiff immobile chest) I have a better posture now than I did before the surgery. One of the methods I used was to lay on my back with my head hanging off the end of my bed. As my flexibility got better, I hung larger parts of my shoulders and even arms off the end of my bed while keeping my thoracic spine just below my shoulder blades and lower back on the bed. I also kept my legs straight and flat on the bed. I only did it until it started to hurt and immediately stopped. Each time afterward, I could do a little more a little longer before the pain started. Pain is your best friend at this time. Heed your 'friend's' warnings. It tells you to stop before you damage yourself.
In addition to the above, stretch your arms outward and back as far as your pain warning allows while standing up. Don't push to the point of agony, just to the point where the stretching sensation only *starts* to hurt a little bit and immediately let up to the point where the pain stops. It sounds slow, but it pays great dividends in a much fuller recovery. Just ask anyone here who didn't patiently accommodate their healing sternums and you'll find long-term trouble with pain and even dehissence (chronic separation of the halves of the healing sternum--not quite certain of spelling) has taken place. Once in a great while these individuals have had to have follow-up surgery to correct the non-union of the bone. On the other hand, people who babied their actual surgical sites during the 6 week limited lifting time while patiently stretching and working with the surrounding body parts found complete recovery of strength the norm. Also, while technically the lifting restrictions are over at 6 weeks, don't go bucking hay or calf-roping. Instead, increase weight incrementally. I was able to carry 20 lbs. at 8 weeks, and didn't attempt to carry full buckets of water for my chickens until 12 weeks; even then I always carried two buckets for symmetrical balance. Now I can easily carry just one bucket with no problem, even at awkward angles. The first trip down the stairs carrying both kids didn't take place until about 16 weeks out. Even 6 months later I noticed my first rock wall (artificial) climb was uncomfortable, but the next time it was better. Try to avoid strong pulls outward such as you hanging onto a tree or pole with one hand while a someone or something pulls sharply on your other hand in the opposite direction across your chest for several months. That's one of the last directions of weakness to heal. Pull-ups and push-ups will likely be the last exercises you'll be able to recover the ability to do as well as before surgery--just be patient. Each time you try something new with muscle combinations not used since prior to your surgery, it will feel strange and a bit uncomfortable. Again time and patience will help. Stretches within reason commonly used will make re-acquisition of physical skills quicker.
I hope this helps. I'm sure you'll be fine. Please keep us posted. I'm glad it wasn't a sternum wire for you. I had to have a tiny bit of a wire clipped off about 5 weeks after surgery, but, aside from a keloid on the lower part of my chest, my healing went fine.
Chris