[Arete314159]

I went with an Erin Condren vertical layout coiled planner, which is very colorful and pretty, so I don't think that is what you are looking for ;-).

However, the same brand has a line of neutral & undecorated planners with blue/black/grey covers. This one seems like it would raise no eyebrows at work: https://www.erincondren.com/camel-customizable-vegan-leather... .

However, they offer fewer layout options in this line than they do in their more popular offerings.

Levenger, as I mentioned, also has some good options, although they are pricey. ARC (I think that's Staples' store brand?) has a line a lot of people buy. Both of these are discbound, which is a choice you either really like or don't.

Filofax & its ilk also have a lot of options that would look fine in a professional setting.

[CRConrad]

They sell "writing tools". I'm old enough to remember when those were called pens.

[Arete314159]

A quick glance at the Levenger website leads me to conclude that if you call it a "writing tool," you can add $30 to the price.

Similarly, if you call the planner cover "vegan leather" instead of "plastic"...