[Costa]

After carrying a CZ, I too just converted to Sig. I got the 320 x compact, but the sight arrangement is the same as the M18, in that it's a rear plate. I was facing the same problem. I wanted to mount an optic for the first time, but did not want to lose my irons in the process. To make matters more complicated, Sig makes a "pro cut" slide that has a rear dovetail cut for sights, in addition to the optic plate. Also, on my BXR3 variant, it comes factory tapped for the RMR optic footprint in addition to the DPP footprint.

If you want to run irons with no optic, I would suspect that Sig makes suppressor height sights in pairs for the application. If they don't, Dawson Precision seems to make a lot of options. I'm sure you've tinkered by now, but the sights/plate are removed by slide disassembly. There are two Allen screws that affix from under the slide into the plate assembly. Remove those, and you're home free. The sight itself affixes through the plate, and the screws actually tap into the underside of the sight.

Additionally if you'd like to run an optic eventually and change your mind, there are a few companies that make plates that either have suppressor height rear sights or dovetails. I got the Bobro engineering plate and like it. CHPWS also makes some plates. For fronts, Dawson Precision makes various heights. For the BoBro plate, they recommend ~.375, but up to .400 "will be fine". I believe the CHPWS plate dovetail option is cut for Glock.

For lights, I was able to snag a TLR7A (which has switch options as opposed to just a button) for about $130.

FCU's are running around $350-400 from what I've been seeing over the last couple of months.

Happy building.