yeah for your situation you may just have to move everything to the SD card and hope for the best because you don't really have many options. If it has USB ports you could try a low profile USB flash drive SanDisk makes 128GB ones that are no larger than a Bluetooth dongle and they are USB 3.0 so they may have better speeds than an SD card.
https://www.amazon.com/SanDisk-256GB-Ultra-Flash-Drive/dp/B07855LJ99/ref=sr_1_fkmr2_1?ie=UTF8&qid=1542839883&sr=8-1-fkmr2&keywords=SanDisk%2BCruzer%2B128GB%2Busb.3.0&th=1