Zwift has become the answer for me. I previously had my bike on a dumb trainer and it was so boring, I just couldn't do it very long. I now Have a new smart tacx Vortex trainer that connect with my PC wirelessly and allows me to ride and compete with others up and down hills and also to ride in a paceline and draft others. It is a remarkable difference, and the resistance changes with the terrain. The difficulty is very similar to riding outside. I have done several rides up to 30 miles and about 90 minutes. I find that the competition allows me to get my heart rate up to 145-160 quite consistently and keep it there.
What I have noticed is that it has allowed me to do this 3-4 times a week and get my summer conditioning back and it has allowed me to keep weight down which is always a problem in the winter for me. If you are serious about really using your bike a trainer zwift makes it actually enjoyable.