As discussed in my shedinar on capacity fundamentals, one of the most common sources of unnecessary complexity in thinking about whether a person has capacity to make a decision is not being clear about what the information is that is relevant to that decision – and what information is not relevant.
For some years, the capacity guidance note the 39 Essex Chambers Mental Capacity Report team produces has had an annex setting out the information that the courts have indicated is relevant (and irrelevant) for categories of decisions such as residence, care, contact, sexual relations and deprivation of liberty. We have now made it a standalone document, so it can be accessed directly. You can find it here.
NB, the courts have emphasised that the guidelines that have been set down are the starting point for considering different types of decision, as the information must always be tailored to the actual decision in question, but this will at least (1) both save you reinventing the wheel; and (2) If your start with the information as potentially relevant (or irrelevant) you will be doing so on the basis that they will be following a path adopted as appropriate by the courts.