mono cartridge vs stereo

Hard to offer any advice without any system specifics. Additional information would potentially be helpful. In my system, a dedicated mono cartridge makes a definite difference with mono recordings.

In a way you will find always the same groups in discussions about that topic.
Group one
They use a Preamp with Mono button and that's it for them
(Mainly they don't hear any differences in general imo)
Group two
They use Mono carts and they stay with their decision.

I tried both ways, Mono button makes the reproduction dead and the tonal colors are completely gone.

Stereo cartridge with Mono records (those with RIAA, let's stay in the area of 1958 and later), works, but the noise floor is very high.

Mono cart with Mono records
Good results, the tonality is right, the soundstage is huge (you need an Arm with VTA anyway, most Mono button pushers don't know that too)

Yes, there are differences in Mono Cartridges, some are real mono, most are shortened Stereo Carts (high output, hum ...)

A mono only cartridge will bring a significant improvement. I have two arms on my TT, one is stereo the other mono. I've found that set up to work best, that way the cartridge alignments are set up correctly.