I had this same problem not long ago, but the other way around.
My front tyres where worn and the rears still had a few mm left.
In the end, I went with 4x Goodyear Eagle F1 non-RFT.
The grip is a massive improvement! Car actually feels stable at speed in the wet now
Id vote for all 4 replacements. IF your front 2 are in really good nick, just sell them to re-coup some of the cost.
I didn't keep my rears in the end, could not be bothered with the hassle. (Wasn't much left on them anyway)