I really like the circular ones. I can stop anywhere and just slide both tips up. No worry about stitches slipping off. A loooooooooong needle would get very unwieldy as you progress on your afghan. Also anything that adjusts, it seems to me, might cause the yarn to hang up as it slides over the adjusters. As it is, I have problems sometimes with the interchangeable tips on my circular set where the tip and the line meet.

I have a few older straight needles that have line attached to them with a stopper at the end. Maybe you could find one of these in the size you need, and be a happy knitter.

-Babka

I always knit with circular needles. I find the straight needles cumbersome. They get heavy on the ends and get hung up on the arm of my chair.