Botanical portrait? Do you mean "still" photography of botanical, or is this going to be photograph of people with botanical background??
Is this going to be outside or inside? What kind of lighting??
I ask all this because they make some difference in what's practical and what kind of problems you might encounter. With any photographs I make with a definite "star" subject, be it people or flowers, I try to achieve separation by not having anything else distracting by them. With nicely smooth and texture free artificial background, this is relatively easy. But few times, I ended up using paper background in not-so-good condition. I was in studio with strobes that didn't turn down so much. That meant my aperture was closed more, and that meant DOF was pretty big. I ended up having texture and crease of background being focus and rather visible. THAT didn't work well. You may encounter similar situation outdoors as well.
If this is going to be a people portrait and be outside in field (botanical), is having an artificial background even feasible?
In other times, I use no artificial background but make sure everything is de-focused and devoid of color that may be distracting. (I see you are doing B&W)
For small stuff indoors, I had used anything from towels, t-shirts, mat boards, and anything else I may have around.