Anyone with a chronic illness? Appreciating friends

I have ME and since getting it 4 years ago most of my 'friends' ditched me. I'm no longer able to keep up socialising and as soon as I wasn't the fun and spontaneous friend they didn't want anything to do with me. Bright side to this is that I found one very good friend who's stuck with me through it all from the start.

How do you show your good friends that you really appreciate them? I tell her all the time but still feel it's an unbalanced friendship because she's always checking up on me, sending me random gifts and just generally lovely things whilst I can't really do much - phonecalls are exhausting and visiting is out of it...

How do you show your real friends how much you appreciate them when your illness stops you from being an equally good friend?