Tunnel - Since you seem to have liked Signal then you'll maybe like this. I've found they tend to go hand in hand. Just don't go in thinking it's exactly like Signal, which happens a lot.
My Father is Strange - If you've never delved into the long family dramas then this one may be good to try as, in my opinion, it's not as makjang as some but still got the family drama elements.
Just Between Lovers - A slow burn romance but since you mentioned you tend to like slower paced shows this one may just fit you.
Strangers From Hell - Depends on how dark you like your dramas since I know this one was on the creepy side, had gory concepts and was gory. It's a great drama if you're fine with that type of thing.
Angry Mom - It's a bit over the top, can get a bit slow and more but it's an interesting school drama concept that I'd say to maybe give a go.
Eulachacha Waikiki - A comedy drama that nothing is to be taken seriously. If you're bored and just want something light and silly this one is perfect.