What to look for in new cat

[BorpBorpBorp]

We're thinking about getting another cat, to keep BorpCat1 company, and because cats are just so great. For context, BorpCat1 is a very laid back but quite small 4yo female. We've had her for a year, and she came to us with her kitten BorpCat2, who died suddenly a few weeks ago at age 2. They spent a lot of time together, and although BorpCat1 got sick of BorpCat2's endless affection sometimes, she does miss him and is lonely.

Any thoughts about what age/gender of new cat to look for to maximise the chances of them getting along? We're not really set up for a young kitten as the house is open plan so no way of kittenproofing an area, and DP and I both work full time, but I could come home at lunch times to check on/feed a cat. What age does a kitten become a cat?

Another thing is colour - do you think the colour of the new cat would make a difference to whether BorpCat1 would accept it?

Any opinions and advice gratefully received.