If you are heating to 300K above ambient, and need to detect such a small resistance change, you are going to have major problems with contact oxidisation and thermal EMFs. You'll need welded contacts of the same metal (and alloy composition) going to an isothemal block for the potential wires, and to use four wire measurement to have any chance of doing this successfully.
Unless you are working on a micro-scale that makes it impossible, a type K thermocouple in a drilled hole in the metal, or a surface one insulated with ceramic wool is probably your best bet.