Which Mountig Base for Sako 85 S

[SERGE70]

I just got a Sako 85 S (Synthetic) with Stainless Steel barrel in .243 caliber and dont know how to choose the mounting base from OPTILOCK https://www.sako.fi/scope-mounts. Can anyone help me with this? what i mean is that they come in diferente sizes depending on your rifle´s model

Thanks in advance

Sergio