I very rarely post, but for once I know enough about a subject to contribute something. So, a few points:
1. At least a couple of people have mentioned this already, but the point seems to have been lost in all the comments: A 3G force, or even 5Gs, isn't going to be all that stressful for someone lying on a padded couch with his feet, his heart, and his head all at the same level. I found it surprising when I learned that astronauts can raise their arms to toggle switches over their heads at 5 G's. The tunnel vision, blackouts, and other stresses experience by pilots doing airplane acrobatics are due to blood pooling in the legs, draining blood out of the head and brain. Even in a Tesla car, we're are not lying flat when we experience much milder G-forces.
I would expect the pre-flight medical checkup procedure for BFR passengers would be similar to what Virgin Galactic has been talking about for its planned suborbital flights. That is, you'd basically need a note from your doctor saying you had been given a general checkup and were okay for some mild physical stress. BFG passengers are not going to need the kind of training that astronauts go through!
2. Solid fuel rockets have a significantly rougher "ride", and a lot more vibration, than liquid fuel rockets, because the solid fuel doesn't burn evenly. It goes in fits and starts.
3. There is no good reason for passengers (or astronauts) to ever experience much over 1 G at launch. A higher G force means the rocket is carrying more fuel than it needs, which means it weighs more than it needs to, which means it needs even more fuel... That's getting on the wrong side of the rocket equation, which is already a very high bar for large rockets to overcome, which is why they all have multiple stages. For example, with the Saturn V rocket which carried the Apollo moon launches, the rocket spent half its fuel just lifting the rocket its own height off the ground.
4. I'm guessing that the comment about solid rockets having a higher thrust on takeoff was a reference to small rockets. Small rockets, such as hobby rockets, get a lot of benefit from the cube-square law; the fact that small scale objects are much lighter in proportion to their size than large ones. With proportionally much lighter weight, small rockets can afford to carry a much higher fuel-to-mass ratio, and thus can develop a much higher thrust (and G force) on takeoff. WHOOSH! (For much more info on this subject, see the autobiographical Rocket Boys and the movie "October Sky".)
5. An SSTO (Single Stage To Orbit) system is of course a very attractive goal, but as has already been said, can really be achieved only with nearly zero payload**, which makes such an achievement a stunt rather than anything practical. You'd never make money without carrying a payload or passengers. Achieving a suborbital flight with SSTO should be somewhat easier, since you don't have to go fast enough to achieve orbit, but if I recall what I've read, you still need about 90% of the velocity to get far enough out of the atmosphere on a ballistic suborbital flight, so I doubt a SSTO solution for a suborbital passenger shuttle is much more likely.
**That is, so long as we are restricted to chemical rockets. If we start using nuclear rockets, such as the experimental NERVA nuclear thermal rocket back in the sixties, then we certainly could develop a practical SSTO system. Unfortunately, rockets using nuclear heating to boost exhaust temperature (and thus boost thrust) were outlawed by the nuclear arms treaties which banned atmospheric nuclear weapons tests.
