If you stick with your Lt-Wt Commander, you'll have the advantage of parts availability for sure, plus that big .45 caliber bullet and won't have to learn the DA/SA trigger...big pluses in my estimation...and the weight on your hip should be about the same, I'd guess. But ammunition is more expensive for practice...and your Commander may not have the tritium night sights that are pretty much standard on Sigs nowadays...an essential IMHO for a carry piece...that said...here are some add'l thoughts on the P225A1.
I've had one for several years now, got it plus 7 mags for less than $700 and in 'as new condition'. I've carried it regularly on occasion.. Of all the Sigs, with the exception of the P365, I feel it has the best grip "feel" of them all. It's a bit narrower than the rest is the reason. Closer to a 1911 which you now own and which is my all-time favorite. That said, you're accepting a 9mm over a .45 and are giving up capacity vis-a-vis a double stack Sig, for that skinnier grip. A big factor for many.
As to the gun's attributes beyond the grip feel....I shoot mine every bit as well as my P226 and P229, I like the night 'tritium' Sig sights, and the ergonomics of the controls. The DA/SA change over after the first shot takes some add'l training if you haven't been accustomed to that mode of operation...but does offer precision that's sometimes lacking in DA only handguns. Too, the decocking lever portion of the manual of arms, is completely different than a 1911 where you re-engage the safety if carried in Condition 1, cocked & locked.
As to carrying it...the P225 that is...there are plenty of good rigs available to chose from. I make my own, and have found that mine fits the holster I built for my P229. I'm an OWB advocate, & dress around the gun depending on destination and climatic concerns. If you're an IWB guy, the P225A1 is a bit thinner than other Sigs so that may help.
All in all, the P225A1 is a great Sig, but recently discontinued however, and would make a great carry piece if you can live with the reduced capacity. As it's been discontinued, stock up on magazines for it before the supply dries up.
YMMv, Rod