Michael C gave you a really nice answer about the speed booster. But I wan to address the other question.
Can anyone give any advice?
Well, stop reading things about the "disadvantages" of a cropped sensor because they are bothering you for "some reason", but it does not look for any particular reason.
Take your camera and shot. Enjoy taking photos, enjoy experimenting with light from a window, from the opposite window, lay on the floor, step up o a ladder.
KNOW your existing lens this is the most important thing.
I am worried the field of view will be too "zoomed" or "cropped.
You already have a 50 mm lens. Is it too zoomed or cropped for your intended usage? you should not just "worry", you should test it.
If you need a lens for a particular reason, which I am feeling is for indoor photography for group shots on low light you could get a 35 mm 1.8 lens, or use a flash.
Is a 35 mm lens for you? You can also find out with your current lens.
I doubt it is about the sensor size.