I agree with you that it is very unfair that some people have to pay for care in old age when others don't, but I'm not sure that there is a foolproof way around it.
When we made our wills, the solicitor mentioned the sort of thing you mean, which is when you each leave your share of the estate to your children with the proviso that the surviving spouse can live there for the rest of their life.
As you are widowed, you wouldn't need to do this, but could leave your house to your children on the understanding that you could live there until your own death.
The most worrying thing (IMO at least) is that this could leave you in a position where you may not have enough of your own money in your own name to make choices about things like which care home to go into, so you would be left with what was available from the council at the time you needed it.
I think that you would also have to live for seven years after doing this, otherwise it could be considered deliberate deprivation of assets, and could be reversed by the courts.
It is desperately unfair, and it is about time that Johnson acted on his pledge to sort this out - he made the promise to do this years ago, but as usual it was a lie.