I’m using some 10G copper sfp+'s from ONTi that i get of Aliexpress. The non HP ones, and run them on 2.5G on a CRS326. The 10G ones autosense 2.5G as the PC is 2.5G, so that’s nice. But after I bought mine back in April, they’ve come with 2.5G a version. I havent tested the 10G ones for temp while running 10G wirespeed as >2.5G i only run fibre, but on 2.5G they run like 52-54C.
Pretty much all their 10G optical SFP’s and Dac cables are indicated to work in an L009 (in forced 2.5G mode).
For low power/temperature/cost You could use a pair of 10G optical sfp’s and some fibre, or a 10G Dac cable.
You will need to force both ends to use 2.5G.