As mentioned, there are some parts you can add to a lower receiver to make the magazine catch, or safety selector, ambidextrous. I do recall seeing an LWRC ambi bolt stop, but I think that was a proprietary piece for their specific upper.
I myself just ordered a pair of Troy ambi safety selectors and magazine release from One Shot Tactical. They also had Knights Armament and Battle Arms ambi bits.
Anyhow, Alberta Tactical Rifle Supply, comes to mind, I do believe their Gen 4 lowers are built with ambidextrous support from the factory, and you'd be getting top of the line product that was built that way. Might give some peace of mind.
I suppose it all comes down to budget and whether or not you want something intended as ambi or converted to be ambi. ATRS, Troy, KAC, BAD, or whatever other flavor you prefer.
If you want an affordable, personalized, AR I recommend Motiuk. I have one of their engraved lower receivers and I love it with the single remaining fiber in my heart.
For a first AR, the world is yours to choose from. A $500 Norc, or a $5000 custom rifle, all depends on how far you want to go and how much you want to flaunt it. I'll say it now though, research what you buy. Some expensive and well-made guns will actually have more malfunctions than cheap guns under less than ideal circumstances. If you get a race gun it might need to be in perfect condition every time or it jams up tight, whereas a cheap Norc might get dragged through a mud puddle without even slowing down. I get a special satisfaction from hearing of people who buy superguns and feel dissatisfied because they themselves are unable to properly appreciate it. Like me, I'm a horrible shot so if I did get a custom ATRS gun I would not be able to appreciate it properly.
A big part of ARs, I daresay THE point of ARs is the components. You don't so much have an "AR" as you do a chassis in which to put various parts. Some work together great, some are less than good ideas, and some will ruin your day. As such, a cheap gun with a few replacement parts might be a much better choice than a fancy gun that's not set up the way you want it. Any part of the AR can be changed, often with only a few minutes work.
My untimate recommendation is to try to get into a store to put hands on an example. Failing that, browse lots of websites. When I first started getting into ARs I'd systematically go through every single dealer to see what sort of options they had. When I first started I didn't even know there was more than a single manufacturer or model, I thought there was only one kind. Now I know of so many I've forgotten more than I remember.
Have fun.
