There are two alternative libraries. AltSoftserial and NeoSoftwareSerial (or something like that, not sure about the exact names).
But you might run into the same issue. Just be aware that there are limited resources (timers, interrupts, ...) in your microcontroller; and you can not (or not easily) share them, especially when using libraries.
If you just need one additional serial port and want to maintain the same footprint as an Uno, you can use a Leonardo.