For the OP, the only recommendations in this thread that will really work for him in terms of the gain and his phono preamp, without getting into complications with a step up, are the Ortofon 2M Mono SE (from Thakker on Ebay) or the Denon 102.
If I was forced to choose between those I'd definitely opt for the Ortofon as it offers a better stylus (although much more critical of setup) and does not have the restricted frequency range of the Denon, which is a bit off-putting for me.
I'm currently using a rebuilt Ortofon MC 20 Super (boron cantilever & microridge stylus) strapped in parallel for mono (no mono switch here) and it sounds very good, but am going to experiment a bit with it soon wired in series instead as I have slightly quirky phono stage (current mode as opposed to voltage mode).
I'm a cheapskate, so if I was to pop for a mono cartridge, pretty sure that I would do the AT 33 Mono, run it for 400-500 hours and then retip it with a very good (boron or sapphire) cantilever and microridge or line contact stylus. I bet that would be an absolutely killer mono cartridge for about $700 all in and give some of the very pricey mono cartridges a run for their money. Unfortunately that won't work for the OP with his phono gain.