So pretty. You have very healthy cacti. Are you in AZ? I grew up in Phoenix. I love your landscaping. I hope you get the answers you need. You might want to edit your post with better tags such as succulent or cactus to hit the right audiences. Right now you used polls but you didn't offer poll choices.

I agree with Jen. It looks very pretty as is.

You can prune cactus if you want to reduce the size. A prunning saw works best used at the joints not in the middle of a pad and bbq tongs are great grabers so you don't risk getting poked. A blue agave would look nice as a contrast in color and form but still keeping the desert look.

Here is an agave, Furcraea macdougali

that I have in my front yard in Los Angeles. However, I do not know whether it would grow in your area. It's hardy in zones 9-11, and if nurseries in your area sell it, then it will grow where you live. It does take up a lot of space and grows to over 25 feet high, but it is pretty dramatic. It is one of the longer lived agaves.