OP absolutely qualifies for a support bubble, but I don’t know how the new tier 4 rule applies to that
It doesn't, support bubbles are explicitly excluded from the new rules, however if you planned to use the extended Christmas bubbling that is largely abandoned. Support bubbles don't have to be formed within local areas and can travel.
You are also exempt from the travel rules if traveling for education or work or caring responsibilities.
In practice everyone I know providing a support bubble for lonely and vulnerable people restricts their contacts as far as possible to ensure they can provide that support safely.
The extremely clinically vulnerable can also form support bubbles but have extra advice around avoiding infection. Unpaid/family carers have also been exempted (but you can't suddenly start a caring role to get around the rules).
its all been a shit show of leadership and management. Confusing, changing and conflicting rules which even the cabinet regularly got wrong when interviewed. Each late change was blamed on "science" which was ignored when inconvenient (like opening pubs because people are so observant of rules after a few drinks, telling people to go back into offices when they could work remotely).
The new variant of the virus has been well documented for weeks now, its not new information and this decision could and should have been made much earlier.