henna - tips on how to use???

I am a 50+ woman who has been using henna once a month for at least a year to color my hair.  The brand name is Avigal.  I use the 2 step method - first color the grey with Red Henna and follow the first application with a second color.  I am satisfied with the color but the texture of my hair is turning to straw despite use of conditoner, hot oil treatments, etc.  The baby fine hair around my face is the most damaged.  Is there anything I can do to restore the texture of my hair?  I like the fact that henna is natural, that I can do it at home myself.  I have heard that changing from henna to chemicals is very bad for your hair and am not anxious to switch.  I started using henna because I was having the same problem when I used chemicals.  What should I do