It depends on what your needs are.
If you're flying with it all the time, and dealing with vastly different temperature and humidity in different airports/countries/venues, something that is both light and insulated that has an option for a humidifier is highly recommended. The Lomax HumidiPro is excellent for this: https://lomaxclassic.com/index.php/humidipro-cases-covers/
If you need to pack it in a bag with other things, Protec makes a Micro case which is about as small as one can get: https://www.northcountrywinds.com/collections/bb-single-clarinet-case/products/protec-bb-clarinet-micro-zip-case-silver
BAM France and Marcus Bonna both make single "trekking" style cases in nylon that provide decent insulation, protection, and carrying convenience with backpack straps. ~$250 from music stores all over the Internet and locally.
If you want to carry music and accessories, especially if you prefer an "all in one" option versus carrying your instrument plus another bag, then the deluxe Protec case might be of interest, and it's only $125: https://www.amazon.com/Carry-All-Compartment-Accessory-Compartments-PB307CA/dp/B0002CZSEY/ref=sr_1_1?crid=35X2R4TA6EF3A&keywords=protec+clarinet+case&qid=1650778123&sprefix=protec+clarinet+case%2Caps%2C68&sr=8-1
Thomann makes a decent waterproof BAM clone for $71 plus shipping: https://www.thomannmusic.com/thomann_delight_case_clarinet_boehm.htm