Use 4 coins and flip it 64 times and write down hex values. Much easier and it will still be random.
It seems to be much easier to do this with 4 coins, that's for sure. I don't know about the entropy concern, though.
You'll need to make sure that you aren't introducing a bias when you select which order to record the 4 coins. It would be best to use 4 uniquely identifiable coins (for example: quarter, dime, nickel, and penny) and always record the exact same coin first, second, third, and fourth.
It could be that tossing 4 coins further decreases the entropy with respect to tossing just 1 coin, I don't know. Anyhow, why would flipping a coin give poor entropy vs a computer?? Is it that people somehow do that in a predictable way, for example, the coin always rotates several times at the most?
There are 2 concerns that come to mind right away.
1. Muscle memory and habit result in you flipping the coins in nearly the same way every time. As a result, the coin flips are biased to land on one side more frequently than the other.
2. The physical environment itself is biased. For example, perhaps a coin geometry or mass distribution is such that the coin is slightly more likely to land on one face vs. the other.
converting that private key to a public key needs a computer, which means entering your private key into a program.
Technically, I think it might be possible to calculate a public key from a private key without a computer. However, it would be VERY time consuming, VERY tedious, AND if you made just a single tiny mistake in a step, then you would end up with entirely the wrong public key. In that case, any bitcoins sent to that address would likely be permanently lost.
With some additional time consuming and tedious maths, you might be able to verify that the public key was calculated correctly. You'd still risk errors though when calculating your address from your public key.