After going down the rabbit hole that historienne posted, I really like the approach that Burrow and Campaign are taking. Basically, high-quality (i.e. durable) sofas that ship flat-packed. Both assemble without tools, and have higher-quality fasteners, so they're easier to disassemble, pack, and move. Burrow's are modular, so you can take a chair, add a section, and get a love seat, although I don't know if they sell separate middle sections. Campaign's are not modular, but still assemble/disassemble easily. Campaign also sells replacement cover sets.
Lovesac also manufacture modular sofas/sectionals, which are designed to be more easily reconfigurable than Burrow's, although that modularity comes at a steep price, and I haven't seen anything (good or bad) about the quality. Joybird is another company making modular sofas with premium quality and higher prices.