With you owning a Shield already, I don't think you can go wrong with a pistol around the G19 size. The shield for days when you are dressed down too much to make concealing larger a simple affair... The larger pistol for when your clothing permits carry, and its big enough to be comfortable in the HD and range use roles.
Other examples in this size:
CZ P07 gen 2
Sig 320 Compact
I am sure there are others in this size as well.
For something slightly larger than a g26, the M&Pc is a good pistol. I have one, and while very close to g26 in size, its just larger in areas that make it more comfortable to hold, without hampering concealability. As was suggested, full size mags work well for when it is time for range or HD duties. When time to set it on the nightstand, drop the mag, and insert a loaded full size... no need to unload.
For HD and range, I prefer larger though, g17, M&P, VP9... etc...
You can conceal them with the right carry style, and if you don't wear very light clothing. Its just not as comfortable and requires more effort and thought. Some would carry better than others... the VP9 is one, maybe the M&P as well, though its slightly larger. They feel smaller than the g17 anyway, and the lines look like they would blend into clothing better... So its an opinion, as I have not tried and compared.
I like firearms too much to only have one myself...