I've been doing strength training as well. As a skinny kid during high school weighing ~116lbs or so, it was a shock when I turned 27 and was hit 150lbs. I was getting tired more easily, stairs were harder than they used to be... I decided then that it was time to do something about it.

I use Mark Lauren's You Are Your Own Gym program (book + companion app), and it's been great. The program is 10 weeks long, it's all bodyweight exercises using stuff you have around the house. There are 4 difficulty settings, and program is 10 weeks long. The app is nice because it walks you through the exercises with videos and timers. I feel like I've got a ton more energy and I'm in a more positive mood more often.

Not having to go out to a gym is a huge plus for me. I don't like gyms much, always feel out of place and like I'm competing with other people there. Plus there's the hassle of having to drive there, shower, drive back... it just adds a lot of overhead to something that needs to be as easy as possible to ensure consistency.