There are apps that let you pose your dummies. Clip Studio Paint, for example, is art software that's like Photoshop, and has a shop built in where you can grab free, or paid, 3D dummies for your illustration or comic panels. You can pose them. If you have an iPad, there's Poseit, which is really intuitive, and inexpensive. There's also other apps. I believe Poser even has anime models. You an use these for every single panel. There's no shame in it. In some of these apps you can even adjust the lighting.
I can draw, but the style I'm using for my upcoming comic is one that I believe anyone could replicate even if they picked up a pencil 2 days ago. I still use mannequin apps because it's way easier to visualize things that way, and they're a guide. I know how much to exaggerate a certain feature in comparison to the ones on the mannequin, completely skipping past the need for character turn around sheets that I find horribly boring. 90% of my first episode was done using mannequins.
Many of the top webtoons I come across have extremely obvious, heavy use of mannequins. No one really brings it up nor questions it. They just want the next episode! ^^
For Perspective / Backgrounds
This is a little difficult in terms of tools. There's not really any apps for this, but there are "props". For example, Clip Studio Paint's shop will have free buildings you can adjust how you want, and draw over, or keep as is (but the style difference will be pretty obvious). There might even be trees you can place, I'm not sure, I never looked.
The good news is that perspective, at least far as 1, 2, and 3 point perspective is concerned, is actually really easy to learn! And that's preeeetty much all you points of perspective you see in a lot of online, non-professional comics. Learn how perspective rulers go, learn the vanishing point/s, how lines go to it, etc, and wallah! Without much practice you'll have stuff that looks like buildings.
Organic forms can be a little bit more difficult, like trees and clouds in perspective, but it's still not as complicated as drawing the forms of people. It won't take 5 years of learning, or even 2--possibly just a month or so if you really go at it.
Another alternative, of course, is to learn to draw. This will take much longer, but it's worth it You can still heavily use guides while you're making your comic, but I would suggest learning forms on the side to slowly build on your skill. One day, you won't need the mannequins except for referencing once in a blue moon. I'm using mannequins for my comics and help from a friend for the backgrounds, and on the side I'm starting from scratch on the foundations of art and drawing.
Edit: The story I'm using for my comic is one that's quickly becoming important to me. I know that the art and the execution will still not be perfect, but as my skill grows, I'll be able to reboot the series later on with improved art. There's no rule against rebooting your comic later on. It happens all of the time. I've even seen it a whole bunch of Webtoons, for comics that end up as paid Originals! With the freedom to reboot, there's no excuse beyond our own mind not to start on it. When it comes to things like this we are only trapped as we believe ourselves to be.