DECIDED that I'm going to use this one FROM NOW.
1) I decided that I'm going to use this one from now.
2) I decided that I would use this one from now.

Are these sentences correct? When we say 'I decided' it refers to the past, but when I use 'from now' it seems to me like it's referring to the present.

Question

DECIDED that I'm going to use this one FROM NOW.
1) I decided that I'm going to use this one from now.
2) I decided that I would use this one from now.

Are these sentences correct? When we say 'I decided' it refers to the past, but when I use 'from now' it seems to me like it's referring to the present.

Answer

I agree. You need to say from now on.
The decision is what is in the past. From now on refers to the present moment and continuing into the future.

Answer

I would suggest that it should be: “...from now on”. Otherwise, in my opinion, it does not make sense. But you can use either 1 or 2.

It could be also be 1 and 2 but using; “...use this one for now”.

Answer

Both are correct. It depends on the context and what you wanted to express.