One other option is that of multiple bonded lines. This means combining the throughput of multiple lines for increased speed. It’s not cheap but you could double, treble, quadruple your speeds, even of single downloads, and in both directions as I have done. Plus the incredible reliability is a huge plus, as several lines can go down but you still stay working with no interruption.
4G would be a cheap option, but speeds may be variable, as you’re competing with everyone else, unlike your DSL.