To get our part-MC a companion...?

Hello. I have a black fluffy cat called Angus.
He's only a quarter MC but has nearly all the main physical characteristics.
He's one and a half.
We adopted him six months ago. He's now settled and loves going outside. We both work FT but he seems to sleep a lot when we're our and keeps himself busy.
He's been a lot calmer since he had access outside whenever he wants, and since we feed him just once a day (he knows when it's coming rather than nagging for a second feed of the day!).
My girlfriend has raised the idea of another cat to keep him company and that that might help him deal with children a bit better in the future...
I'm a bit worried another cat will upset him just as he's finally settled with us.
He's very shy and as a kitten we think he was left alone at his former owners' house during the day. Being moved from home and new owners must be traumatic too.
He's now fine with us (it's still a struggle to brush him though!) and most adults. He just doesn't like my girlfriend's sister who, being a 'cat lady' with lots of Siamese was too forward and went straight to him and picked him up when he was quite new with us. He hasn't forgotten...!
He's settled in a routine now but quite guarded - often checks around his cat flap and keeps his distance from strangers and other cats.
He goes outside a lot but us very lazy inside. His wait shot up to 5.5kg do we had to lower his good to 40g dry and half a wet pouch a day. Now his weight is slowly coming down and he's never squeezing for food either.
I've read about how it's best to gradually introduce new cats to each other, and that it's best to get another cat of a similar build and age - we'd go for a female.
But what do people on here think? Would it be worth a shot for the long-term, or not worth the risk of upsetting him and really stressing him out.
Has anyone on here had a MC with similar character traits etc
Any advice would be appreciated.
Thanks very much.

hi John - welcome to the forum!
well about introducing cats to each other, I'm a ferm believer that there is no right and wrong -
MCs are supposed to be really social animals - this being said, mine absolutely hates everything and everyone new introduced to the household - my father in law came to stay with us for one whole month, 30 days, and only after 28 days did she stop hissing at him on sight.
BUT she's an exception, and hopefully you haven't got one of those.
The trick, I am told, is 1) there doesn't seem to be any other trick - people have suggested gradual intro, exchanging blankets for scent and things like that - others are adept of "thow them together and see what happens" - from what I have observed on the forum, both techniques seem to work the same.
2) give it time... it is very likely that they will not say hello welcome to my home, it will take time and hissing and spitting - but so far on this forum the longest that it seems to have taken was about a week I believe.
3) don't stress - I didn't know that - I stressed a LOT when I had to leave for the first time her at the cattery for 3 weeks - now I think I have the result, a social-phobic cat.

Thanks Alekto.
In the end we have got a shy ginger and white kitty from the cat rescue centre.
We've had a few face to face meetings and taking things very slowly.
Angus, our part-MC, is a mardy scaredy cat at times. Bonnet is used to other cats and should be okay, sadly that's because I believe she was rescued from a dingy flat that had loads of other cats in :-
Here are a few pictures of our Angus by the way. We think he's quite spectacular!

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Hi,

I've just joined the forum and happened upon your post. I just wanted to say how beautiful your Angus is. It's amazing how much more glamorous (to me, at any rate) a black cat appears who has beautiful long and fluffy fur. A very regal kitty indeed.