So looking into Apothecaries I have some ideas
Forge world:

This is cool because it shows me the Apothecary is really wearing a chain fist with the geneseed extractor as part of it. So for a terminator that would be pretty cool.
Now the Dark Angels command set had an apothecary in it:


And while it isn’t a chainsword, it looks pretty close (drill bit, gene extractor, chain bit). Now I found one


So the obvious answer is grab the mini! (working on it). If not model something like it.
Ok, so the Dark Angels seem to have the best bits! So firstly I ordered this to give the terminator something to carry.

I also ordered:

For the back-mounted injector (not sure I love them) but the hip vials will look cool on the Terminator.
Now another great option is use the apothecary Primaris and modify it to be a terminator like this person did: https://www.reddit.com/r/Warhammer40k/comments/1ha95j9/an_apothecary_biologis_in_terminator_armour/

Not a fan of the Apothecary gum bit, but the rest of the model is excellent, and I like the apothecary bits on the Terminator.

