What's better than a Non-Disclosure Form? Is there something legally stronger that's also practical or easy to set up?

I have a cool, useful, practical and clever idea for a design for a leading businessman (no names) but want to ask him if he'd like to legitimately buy it from me - but - I cannot afford to tell him in a message/email/letter for fear of him just stealing it and finding many ways not to pay me for it.

Is us both mutually signing a non-disclosure form going to keep my idea safe from him using/taking the idea or is there something much stronger, legally speaking?

I need him to be legally duty bound NOT to legally worm his way to stealing my idea I have for him, but I do want him to buy it from me if he likes it. Any concise advice welcome, thank you.

I'm in the UK but he has offices world-wide, so who's laws are the most relevant? Thanks.

Is there something legally stronger than a non-disclosure form at all? If so, how do I get one and how do I get it to him to sign it?

Lastly, I have NO capital, no way to GET capital and absolutely no way to pay for any patents etc. I simply want to impress him enough so he pays me fair n square and takes it legally so I am not out of pocket at all; I'm fairly confident he'd stand to make a lot of money from it as its currently not in his design repertoire.

Please get in touch if you can solidly advise, thanks!