I know some pretty helpful stuff!
at least it helped me personally to get to know the language so well that I enjoy k-dramas without translated subtitles ;)
so here are some recommendations (which are by the way all for free!!!) :
some useful apps:
you maybe already know about duolingo... but I would like to mention it as well. I think that it can help you to get to know new vocabulary, but you shouldn't pay that much attention to the grammar stuff.
concerning grammar, but also great for vocabulary is the app called Lingodeer. Here you get a perfect introduction into the language with small sentences which help you to memorize new vocabulary and understand more and more grammar. you also get to hear those sentences which I find very important!
Next there are multiple apps that you will find if you type in "세종한국어" at the app store. there are ones for beginners, grammar or vocab focused and when you reached some fluency there is also one that works with small articles.
now let's move on to some helpful websites:
the 세종한국어 apps are made by the 세종학당 and they also have a website. there are textbooks and work books available for free as ebooks, as well as some information about Korean culture and a bunch of recipes of Korean food. (even though I find this website pretty help full I needed some time to get used to the handling)
another website called "talktomeinkorean" is the best thing you can find if it's about grammar!!! I only can recommend you to have a look into it. they have lots of episodes in which they explain everything starting from the very beginning until pretty complex structures at the end. there's always a podcast version and you can check the PDF which normally includes the transcript of the conversation and a short overview about the grammar newly introduced. they also publish the podcast on Spotify so that you can listen to them while doing something else! (They also sell additional stuff in form of books and work books if you want to practice more. I think you should take a look at their store which is also directly on their website)
If only listening isn't enough for you, they also have a YouTube channel where they 're constantly uploading new stuff. Have a look and you'll like it for sure!!!
those are manly the pages and apps I used and even am using right now.
but I want to suggest you other methods as well:
how about listening to some Korean music and having a look at the lyrics. even though sometimes the sentences aren't like spoken Korean, you can learn new words by that method and especially get familiar with the pronunciation.
maybe even better are videos or k-dramas. Have you heard about Viki ? it's an app where you can watch a huge amount of k-dramas for free with subtitles in many different languages. English us always the first one made by the fans, so you wouldn't have to wait for long even for the most recently uploaded episodes.
okay I think that should be enough input for now. Have a look at the things you're interested in and if you have any further questions about my recommendations, go ahead and ask me ;)