Sorry for your fall! My advice follows… I’m a neurosurgeon who consults in sports-related TBI for the USEF, NFL, and others so this issue is something I lecture on in an official capacity frequently. I’m assuming that you have a concussion only and no structural brain injury identified on imaging or significant past medical history.
First of all, no need to take 4-6 weeks off. All the literature is quite clear on this. After a concussion you need to rest (no athletic activity or high risk activity) until all symptoms have cleared and you are back to normal. At that point you resume your activity in a stepwise fashion. For most equestrians that might entail a day of vigorous walking on foot for a couple of miles, then a day of jogging or other light cardio, then a day of full cardio. If all feels good, get back on and add a light day of riding, and up the effort to your usual effort over the next few days. If no symptoms recur, you are good to go. If symptoms recur, STOP, rest, and return to the beginning. The process should take about a week.
This is called “stepwise return to play” and is highly validated in many sports. Random fixed time periods of avoiding activity is, honestly, old school and not evidence-based medicine.
Average time to become symptom free (if you really rest) is 3 days. 80% are symptom free within 1 week of concussion. A very small number are never symptom free and can not ever return to sport. So you have to let your body be the guide.
In terms of helmets, in my educated opinion, there is no commercially available ASTM equestrian helmet that is any safer then any other. Find one that fits well (critical) and that you like. Price is all about style, not safety, unfortunately. Treat it well and replace if it is left in the hot trailer, has a significant blow, etc. for all these reasons I tend to ride in helmets that run around $40!
Hope that helps. My non-COTH name is Lola Chambless, MD as most in here know, but in case you were worried I was an internet quack 