Dear Alex,

A widely used measure is by Sheldon Cohen of Carnegie-Mellon U.

It is called the ISEL, Interpersonal Support Evaluation List.

I believe there are four subscales: Tangible Support, Emotional Support, and Instrumental Support (not sure of all of these....).

I have used these measures on 123 older adults caring for a spouse with AD and 117 matched adults caring for a spouse without signs of AD.

I like these scales not only because of what Sheldon reports about them, but because I know from my own analyses that they have good internal consistency (.85 and higher) relative to their intercorrelations of .40 or so.

I especially like these measures because I was able to test an interesting H about the differences between usefulness of tangible vs. emotional support for physiological function in persons with lower vs. higher incomes. The H was that tangible supports would be more related to physio measures in lower income people than higher income people. This H was not rejected. I find this to be a fascinating way to study social supports. The paper was published in Health Psychology.

Take care

 http://www.apa.org/pi/about/publications/caregivers/practice-settings/assessment/tools/perceived-support.aspx

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The  Duke UNC Social Support Scale measures some of the components of social support you mention...although it may not evaluate the type of companion support you want to measure.  Can you provide a definition of what you mean by companion support? 

You might want to consider the Family APGAR. You can see a copy of the tool here: http://www.stritch.luc.edu/lumen/MedEd/family/apgar1.pdf