Gerty, I believe you have all the ingredients at your disposal to create some nice self portraits. It's just a matter of some slight rearranging. You already have a large light source by way of the window in your front room. Depending on the time of day, you may need to diffuse it further by adding another layer of material. A white bed sheet or clear plastic shower curtain will do for this if the light is too strong coming in. You will want to have your camera positioned so that the window is to the side of your camera. But let's take a step back.
Being a heavier set person with a round facial features, using short lighting should give you a better look. This means that the shadowed side of your face should be towards the camera. It creates a slimming effect. But at the same time, you do not want deep shadows without any detail on the shadowed side. You can better your chances by using a reflector opposite the main light (window). A simple piece of white poster board from your local craft shop will supply this or even a baking sheet will suffice. Of course, you will need to position this so that it will redirect (bounce, reflect) the main light back onto your face. This may be trial and error until you hit the correct angles. So if you're standing perpendicular to the window (on the left) and your camera is parallel with the window, turn your body about 30° away from the camera.... move your left foot back 1/2 to one full step counter clockwise (anticlockwise).
In portraiture, the camera position should be even with or slighty above the eyes. With heavier persons, you may want to raise this slightly more. This also has a slimming effect. When in your posed position, try leaning forward at the waist. I would also suggest to point your chin forward as much as possible without giving a strained or unnatural look. I also suggest to my subjects to try and take their ears towards the back of their head. I know it sounds funny, but it opens their eyes and helps smooth out their skin. Bring their hand up to their chin, but not actually placing any weight on it, is another little trick to help obscure double chins and thick necks.
One last thing for self portraits. Find something, anything, that you can use to pre-focus where you will be positioned. Focus on that and turn Autofocus OFF on your camera, then move that item out of frame. I'll use a marker on the floor to make sure I hit the same position. Make sure you have stopped down your lens enough to allow for some slop. I would suggest to set your aperture to not less than f/5.6 uo to f/11.
I hope some of this dribble is of benefit and I certainly don't mean to sound offensive. There's more, but this is a start plus I'm tired and have to edit some photos myself. Good luck.