前より良いよ。って英語でなんて言うの？

1. You state that you feel much better than before.
2. To be on the mend = To be improving.
   "After her operation, Sarah is now on the mend."
3. On the road to recovery = recovering; getting better; improving.
   "It's been two weeks since her surgery, and she is on the road to recovery."

"I feel much better than before."
This means that you have recovered since the last time you would have spoken to your friend and you're feeling better.

"I'm in a better state than before."
state : the particular condition that someone or something is in at a specific time.
e.g I was in a bad state last Spring when I got the flu.

"I'm almost as good as new."
To almost be as good as new is to be in a very good condition or state; close to the original state again after damage, injury, or illness.

You can also say :
" I am in much better shape now.

"I am feeling much better than before." will put across to someone that you have gotten better from your cold, since the last time you talked to them, but are still a little sick.

To express that one is feeling better than they did previously they say the following;
I feel rejuvenated.
keyword: rejuvenated-feeling renewed.

I feel much better than I did previously.
keyword: previously- prior to, earlier

I feel I've recovered from my cold.
keyword: recover-to get better

One may also simply say. I am much better than I was the last time we spoke.