After rereading Dostoevsky a few times, I wouldn't try to find someone "similar" - you risk being disappointed, because nobody writes quite like he does. Better to pick something in the same ballpark, but with its own flavor. Camus, for instance, has a completely different style, but he talks about absurdity and the meaning of life just as piercing as Dostoevsky talks about faith and doubt. "The Stranger" or "The Plague" - shorter than his novels, but philosophically they hold their own.
From Russian writers, you could try Rozanov or Shestov, if you're up for a completely different format - these aren't novels anymore, but philosophical essays, though they've got just as much internal intensity. But I can recommend Bely's "Petersburg" - there's genuinely that similar tension, symbolism, the same obsession with the main character's ideas. Just a heads up though: the style is modernist, the text is very dense, heavy. Not for quick reading.
Here's the catch though: if you're looking for "Dostoevsky, but different," there's a risk you'll come back to his works again in a couple of months. Maybe it makes sense to take a little break from philosophical novels altogether first, then pick someone from a completely different universe - that helps you come back to Dostoevsky with fresh eyes afterward.