Hey, that's a very hard decision to make... I know it is.

I'm no doc, but I will just give you my advice: do not start prednisone.
If you're in that state where you still can choose, you do have symptoms of course but near a crisis, do not do it.

I've been there in 2010. Yes or no to those medicine. I was in the state you discribe. I couldn't do much, but I still was able to do little things. They said: you will feel wonderfull, it's such a miracle drug!
However, they kind of forgot to tell me that once I started the prednisone, getting rid of it was almost impossible: fat chance I'm on it for the rest of my life. Which kind of s*cks, considering the side effects. I've already had a steroid psychosis, have diabetes and much more.

If you're prone to hart disease (which you seem to be), another no to prednisone (of course, of you have to you have to...). It can give you diabetes, high blood pressure, high cholesterol, weight gain, weak heartmuscles and can give you these food cravings (you think about food and HAVE to have it). Which all gives you more chance on heart diseases.

Of course, this doesn't have to be the case. Maybe you will get loads better with just a tiny bit prednisone, without any side effects. No one can say.

However, I think there may be possibilities in trying immunosuppressants. Those can take a long while to start working, and do not always work. Azathioprine is most common for MG. For me, this didn't do anything. MMF (cellcept) is another, but this one can give you high cholesterol. Methotrexate is another one.

Most of them do not have side effects like weight gain. If you do gain weight because of one of them, it's mostly because 1) your symptoms get better so you can eat better or 2) you hold on water because you have kidney problems or high blood pressure or something.
But losing weight / being less hungry is a more common side effect.

Anyway...immune suppressants can have side effects, do not always work.
But with those, there's just no way to predict which one will be good for you. They do tend to take a while (sometimes even over a year) to start working.

For me:
Azathioprine (imuran): no effect at all. No side effects either. Used it or 2 years.
MTX: it worked very quickly, but it caused liver damage so had to stop. Used 8 months.
MMF (cellcept): no effect. Tiny side effects: higher LDL levels. Used 2 years.

Good luck, it's a very hard decision to make...