You could make the cluster less bulky with fewer stitches in it. Don't know the directions in your pattern for the stitch, but just do one stitch less in the cluster and see how you like it.

I knitted a beautiful afghan for my sister using two strands, and it had two panels of all popcorn stitch. It was really pretty, but I used Caron Simply Soft, which makes up so pretty too. It is not a bulky worsted, and I am sure that made a difference.

Of course, you could use another totally different design. Some small cables would look nice using either 2 or 4 stitches. Don't make a big thick one or it pulls the shape of the strip. Seed or moss stitch gives a nice texture. Basket weave would look nice too--p4, k4 for about 4 rows or so, then do the opposite for 4 rows--k4, p4. And repeat for the whole strip. Use 3 or 4 stitches and rows in the basket weave and see if you like it.

The cluster is P3 tog but do not drop sts off lh needle. Yrn and purl the same 3 sts tog again. Slip sts off lh needle.
Cluster st pat
1st row: with color A, K1.*Cluster. K1. Rep from * to end of row.
2nd row: with color B knit.
3rd row: with color B K1 P1 K1. *Cluster K1 Rep from * to last 2 sts P1 K1.
4th row: With color A knit.
The afghan consists of patchwork strips in squares of various colors like a quilt.
The strips are as follows:
With color C cast on 22 sts. Work 26 rows in box st pattern. (K2. P2 for 2 rows and P2 K2 for 2 rows)
With color A knit inc 3 sts evenly across.
Work cluster pattern for 25 rows with color A and B.
Row 53 with A knit dec 3 sts evenly across.
With A work box pat for 26 rows.
Hope this isnÂt too much info. Thank you.
What do you think small cables would look like with the two colors. Would garter stitch in two colors look alright?

Why don't you work up a little swatch, with small cables, to see what you think of it....ditto for two color garter stitches. (and, you're the only one that needs to think they look 'alright'......your afghan, your decision).