I also use Duolingo and I also use Peak. Peak is an app where you train your brain everyday by playing educational games. After some time you can see improvement in some areas. It can improve your focus, mental agility, memory, language, emotion, problem solving and coordination. It is pretty similar to Elevate but I prefer Peak. You will play about 4 games a day (maybe more or less it depends on you).
I use duolingo also but it's just good to reinforce the vocabulary, not very nice to learn grammar and such. A good app for vocabulary also is Drops or some flashcard app (anki for example). You don't need to stick to books always, there are many great channels on YouTube, sites (i can't recommend any because they're specific for the language, i know many sites which teaches russian, japanese, english, but probably they're not the languages you're learning), or you can watch some series/movie in the language you're learning, listen to music/audiobook and read the lyrics/text and etc