Left-hander, here.
To my way of thinking, a lefty-friendly gun is where the controls are easily reachable and can be easily manipulated by the left hand fingers. That either means a gun with sufficiently large and easy-to-use controls where you learn to use them no matter where they are, or a gun with controls flipped to the other side for lefties. As a lefty, I've used both and don't really care which one I shoot. The one thing I can't deal with is a semi-auto pistol where my fingers simply can't reach or can't manipulate the controls. Everything else, I feel is fairly "lefty friendly," even though the controls might not be flipped onto the right-hand (lefty) side.
My first firearm was a Browning BDM 9mm pistol. With a large, easy-to-use decocker/safety lever that was ambidextrous, the gun was simple to operate with either hand. The gun isn't made any longer, but Heckler & Koch has the ambidextrous thing down pat, these days.
If really looking for a lefty-friendly semi-auto pistol, check out Heckler & Koch's P2000, P2000SK (compact), P30, USP, USP Compact pistols. The P2000 series has an ambidextrous slide release, no external manual safety lever or decocker. The USP's come in a variety of flavors, but the controls can be switched to the other side if you choose. Extremely well made, reliable, accurate. Available in 9mm, .357 SIG, .40 and .45, depending on the model.
For several years, I had a CZ P-01 9mm pistol. It's a SA/DA action, with decocker lever on the left side. All the controls are large and easy to manipulate. Even being lefty, I found each lever to be simple to use with the finger of my left hand, and when shooting righty everything was accessible with the right thumb.
IMO, it essentially depends on your hand and whether you've long since adapted your shooting to accommodate right-handed pistols. So long as a pistol has larger, easy-to-manipulate controls, I think it's reasonably simple to use as a lefty. That's assuming your fingers can reach the controls easily. Many lefties report easily being able to use the Glock 19, various SIG pistols, and other similar models that have puny, hard-to-reach (for me) controls. It all depends on you and your preferences.
That being said, I simply love certain pistols for their ergonomics and great feel in the hand, which also includes the ability to reach and operate the controls (of course). If looking for a new pistol that multiple people are going to use, I would also consider the Kahr K9, P9, CW9 pistols. The K9, in particular, is extremely well made with great ergonomics. Or, the CZ 75 series (including the PCR D Compact and the P-01). Each is excellent, assuming you both can reach the controls, since it's a bit larger frame. You have the 2075 RAMI and SP01, so you know what I mean about the CZ's. If you require ambi controls, consider the H&K pistols. All are exceptional.