2nd cat, what to get?

have a 4-yr old girl, Siamese mix, very well-behaved and loving.

thinking about getting a friend for her since I'm gone all day.

vet recommends a kitten but I like adult cats that come already trained and are less destructive.

any advice on what I should get?
breed?
male/female?
age?

I have 5 girls and they all get along.
Meeko and Coco met each other when Coco was 10 and Meeko was 2.
Meeko hissed at Coco non stop and hid when they first met.
Now they are great friends.
A kitten I think would be a better choice then a older cat.
A older cat might fight with your cat and be set in its ways.
My sisters 3 year old cat destroys everything so just because a cat is older it does not mean it will not destroy things.
I got my last ktten in Dec at 4 months and she was accepted the first time they met even though she is bald.
Do you want a purebred or one from the pound or a rescue.
You need to decide on that first.
Do not go by sex.
Go by what you like.
Maybe go for a older kitten like 8-10 months old.

one from pound or rescue is fine.
I've just heard that kittens need a lot of attention at first and I'm not here most days to provide that.

I would not get a kitten for your 4 yr old... Too much energy, plus it would need a lot of attention on your part as well.
I would get a laid back young adult - 1-2yr old; probably closer to 2... If you go to a pound, ask them for a calm, relaxed, non-alpha cat. A rescue might match you better as far as personality goes.
Have you checked petfinder.com?

no but I will... thx for advice!

I am sure you will find acat you like.
I have a 3 year old cat that still is hyper.

Good luck, my cat acts like a kitten and is an adult
I agree go by what you like, don't be too set, not in color, size, age, or even gender. But more so purrrrsonality, of both kitties. And do proper introduction.

I found one I like but it's a 4-yr old male that's bigger than my female... and the vet recommends getting one a little younger and smaller to (hopefully) avoid dominance/territorial issues.

anyone agree or disagree?

IMO it depends more on the cats personality... Bugsy, my second cat, is much bigger than Lucky, my original cat, and also older... I had no problems - Lucky is definitely the boss, I don't think she ever realized Bugsy is so much bigger!
I would just get a laid back cat, a cat that is not a natural alpha cat...

Yep, size has nothing to do with dominance. Some cats seem to have something to prove because they are little.

Does the male have any history of how he behaves with other cats? Is he in with other cats? If you can ask or witness how he socializes with others it will be a great help. For example, if he walks up to another cat and happily greets them, rubs his whole body along them it could mean he's fairly social and how he behaves towards a dominate cat is important too. Like dogs cats will roll over on their backs to show they're more submissive.
Cats like my Tomas will do this instantly to stave off any disagreement with my other two. A sort of "hey look guys, I don't want to cause any trouble".