If you just want to plug a keyboard into your modular, buying a plain Arturia Keystep will be cheaper than any MIDI to CV converter in Eurorack.
A Keystep Pro would be even better and would probably streamline your sequencing/producing here by giving you both the keyboard and access to multiple sequencer tracks, but that is a bit of a price jump from the Keystep or even the mighty Beatstep Pro that you have (plus the Keystep Pro lacks all the cool knobs).
The regular Keystep is your best bet here for just adding a single keyboard, though. It's cheap, has its own CV connections, does sequencing/arpeggios well, and can even be used as a MIDI to CV converter if you want to control pitch and gate of a module from, say, your computer. MIDI to CV is expensive to do in the rack and none of the cheapest options give you much mire power than a Keystep