A bellows and a rail serve two different functions. A bellows changes the distance from the camera to the lens. A rail changes the distance from the camera and lens to the subject. I think a rail is what you would want for this.
I agree: the closer you get, the more difficult framing and focusing become because the distances get so small. The way I handle images like this one is this:
--I get the tripod roughly where I want it.
--I use a rail to make small changes in distance to get the image the size I want. This requires that you get approximate focus.
--I use a geared head to make small changes in rotation
--I do the final focus with the lens barrel.
You could do it the other way around: prefocus approximately to get the image approximately the right size and then use the rail to fine-tune focus. I am used to doing it the other way, and I know from practice how much to rotate the lens barrel to create a stack.
What I did before I had that gear worked fine, but it required patience. I would roughly focus, see how far off I was in any direction, move the tripod or swivel the head, and repeat. If often took a bunch of iterations. Once the framing and distance was right, I just used the lens barrel to make the final adjustments to focus. My problem is that I am really short of patience.
Looks good as is, but I agree a rail is the way to go. Have you tried looking on eBay for a used one? I did a quick check and there were several at not a bad price.
Or you can cut the flower and place in a jar on a table Brian
With your lens set at 1:1 move the flower towards/away from the lens whilst looking through the viewfinder until focus is sharpest at the plane you want.
But, I agree this is where a rail really can help.
Brian, does the head on your tripod have an Arca Compatible clamp?
With an Arca Compatible clamp, you can get an inexpensive long camera plate:
https://www.ebay.com/itm/200MM-Lens-...MAAOSwX~dWjhU4
and you can use this plate for sliding the camera back and forth or side to side (one or the other) in small increments.
If you do not have an Arca Compatible clamp, most tripod heads can be retrofitted with an Arca Compatible clamp such as this one...
https://www.ebay.com/itm/QR-120-Clam...MAAOSwHIlZwIey
which is great for moving the camera to and fro or side to side.
Even a standard size Arca clamp will work with the long plate.
https://www.ebay.com/itm/Manfrotto-C....c100705.m4780
Of course, a focusing rail is more versatile but, the Arca plate will work.