Sometimes, some good ol' solitude feels good man.
What does good old mean, and how do you usually use it in context?
Good old is whatever is liked or admired or familiar and comforting which
remains from the past, still functioning as it always did
My good old 63 Cutlass
Good old Jimmy Carter
The good old Chicago Democratic machine
existed or obtained in the past (or you believe existed or obtained in the past) -- the "Good old days" -- but is now neglected or vanishing or gone
The good old tradition of liberal education
The good old portable typewriter
However, the term is almost always used ironically today:
Good old Bob, always finds a new way to screw it up.
Good old VHS had absolutely unique reds and oranges.
The good old Know-Nothing party seems to be making a comeback.
Good old boy is a specialized application of the term: a well-regarded and 'connected' man of the politically dominant yeoman class in the US South. This must be distinguished from the British old boy, originally an alumnus of one of the prestige 'public' schools, by extension a well-regarded and 'connected' man of the political and financial elite. The two exhibit very different manners and mannerisms.
You could perhaps use the definition that FreeDictionary gives, and apply it here.
I use good old to mean something that one used to know, and that is no longer seen as much (or at all) in the present time.
The FreeDictionary mentions good old days - past times remembered with nostalgia.
Another entry which is somehow separate:
back in an earlier time which everyone remembers as a better time, even if it really wasn't. Back in the good old days, during World War I, they used real cactus needles in record players. The good old days didn't start until they had indoor bathrooms.
Though Cambridge mentions only the positive part:
If you talk about the good old days, you mean a time in the past when you believe life was better: I wish my grandma would stop going on about the good old days.
In your case, I would interpret good old solitude to be like a traditional 'therapy', that none from today can substitute.