What are some of the most reputable tools for doing this? Something that many users have used for years without issues.
Note: I don't want to rely on only one of those two. I want to combine both.
Some software and
hardware wallets have already implemented the feature you are asking for. The way it works is you add several bytes of your entropy by flipping a coin or rolling dice and, in case you didn't provide 256 bits of entropy manually, then an in-built cryptographically secure pseudorandom number generator generates the rest bytes.
Check this, for example:
https://bluewallet.io/docs/manual-entropy/Bluewallet is an open-source non-custodial wallet, so everything can be found on their Github page:
https://github.com/BlueWallet/BlueWallet#readmePlease note that unless you're a skilled programmer capable of verifying everything yourself, including the source code behind the seed generation mechanism, you will always have to rely on and trust others when interacting with software. If you don't want to trust, then generate everything manually.
I agree that trust will always be needed somewhere. However, I look forward to critiques of what I now write:
In my (current) opinion, there is a
huge difference between trusting reputable software, cloning it, transferring it to an offline generic-purpose laptop, and running it there -- versus trusting a hardware wallet. The latter is a specific purpose device. It's a single point of failure where all you need are a few rogue employees in the hardware manufacturing unit rigging the hardware - independently of any firmware installed on it, rendering any efforts of open-source, signing, and reproducibility (Gitian) impotent. I would not be surprised if one day, oops: thousands (millions in a few years) of people running one of the most popular "ultra-secure" hardware wallets suddenly lose their funds.