I took advice here, got a basic Grado Mono Cartridge, elliptical stylus on aluminum cantilever. Definitely better than playing mono lp with stereo cart, even if preamp has mono mode.
Next, I searched for an at33 mono body with broken cantilever. $38. yahoo/aledo. shipping was more, total just under $100.
Gave it to Steve at VAS, had him put boron cantilever with advanced stylus. Terrific, and less wear to your lp grooves.
I wanted to go stereo/mono instantly in a listening session, i.e. Jazz greats, late and early lps.
Decided two tonearms ready to go. One of them with removable headshell to switch my mono and stereo and friend's cartridges.
A related issue is how you select/send either arm's signal to your phono stage, and if PASS to use MM cartridge or MC
I went for JVC Plinth PL-2 for two arms, and ended up adding a 3rd compact arm.

Best stereo on the right long arm, best mono on the left; removable headshell rear arm: height/vta super easy for any cartridge.
Luckily, I went SUT (step up transformer) to MM Phono Stage. SUT has 3 front selectable inputs, 4 various loads for MC. rear out to phono stage so you never change cables. fidelity research frt-4

entre-100 similar features
I suggest one great TT, two arms, two great cartridges, option to change cartridges on one arm