As Joanan stated, you need to take a risk to do your own company. You try to secure your salary by a consultant contract but I doubt that will work - at least I would be surprised.
It as well depends how open minded your relationship with your employer is. I did that once offering to create a company and offer them actually a product they need which I would do with another person who was working for the company. The company did not take it but took a competitor product but it did not harm any relationship between me and the company in the end.
The bigger the company, the more corporate, the more difficult this might be. So you need to know.
The IP might be an issue but as it's not something that is part of your work but just a tool to make your work more efficient then I would be surprised if it would be an issue.
And even if, you just need to change a few things later to make it a bit different to the original idea - that will happen anyway when you receive feedback to your product.
Of course you can ask for a consulting contract but only if it's feasible. Nobody will give you the money for a consulting service where the purpose is just to get your income for one year.
And about your options:
B. is only valid when you work for an investment company that invests into startups otherwise this won't work.
A is a good option but you won't get the consulting but with an LOI you might have good chances to get external money.
C is a viable option but of course you need to raise the money. I would probably go for an accelerator in that case - from what you write it sounds to me that you need as well advice along the way building a company. - I might be wrong though.