A Stouffer step wedge (and Ralph would recommend 31-steps) can be all you need to get started.
Add ANY meter that you can use as a "comparator", and you can create a densitometer precise to one "step". Mike Wilde explains how you can meter your negative and then find the step on the scale that meters about the same. I used to do exactly that.
I was able to get densities of my 35mm negatives by customizing a negative carrier for my enlarger. I cut a small window and sliding slot in my negative carrier to hold the Stouffer scale. I used an Omega CS-10 comparator at the easel to cross-reference significant points of the negative to the Stouffer scale.
This is only precise as your Stouffer scale, for example a 21-step scale is only precise to .15 density.
These are the working steps:
1. Place negative in enlarger and turn it on.
2. Null the comparator on thinnest part of neg.
2. Pull out negative carrier to reveal the first Stouffer scale step.
3. Slide Stouffer scale until comparator indicates null.
4. Note the Stouffer step showing in the window. The corresponding density of the step number is your d-Min.
5. Push in carrier, find darkest spot of interest on the neg and null the comparator.
6. Pull out carrier and null again to find the d-Max Stouffer step.
An advertiser here offers an enlarging meter that I believe works essentially the same but can read densities more directly and precisely.
Not long ago I took a chance on a used TR-524, Transmission and Reflection densitometer. I got it working with little effort, but it was a low-risk purchase for me because I have work experience using and maintaining graphic arts prepress equipment.