[Closed] MTB 9 and 10spd front mech compatability

I need a new front mech.
I'm currently running 3 x 9spd with the big front ring removed and the limit screws dialled on the front mech so its effectively 2 x 9.
I'm assuming I'll have to change to 10spd before the new front mech dies and will be going 2 x 10.

So, can I buy a 2 x 10 front mech now and expect it to work with 9spd chain / chainrings and a 3 x 9spd shifter?
Or do I need a 3 x 10 front mech to work with the shifter?
Or will 10spd front mech not play with 9spd chain / chainrings at all?

I know it would be easier to change it all, but that's not going to happen whilst there is still life in the cassette / chain / rings.

thanks