I am not sure to understand your question: is it about the cost of a bag, or is it about how many bags you are allowed to check with your ticket? The answer of the first question may depend on the second, as usually the price of a 2nd bag is higher than the price of a 1st bag. Regarding your check-in allowance, KL should be able to tell you exactly about it if you ask them: if not, try to hang up and call again. I would though expect Transavia to be stricter than KL on this, so if Transavia tells you you have 1 bag (per booking? per pax?), you could be confident for the whole trip. But it is better to have a confirmation from KL for the outbound flight, as you will check with the first operating carrier (KL or its representant at GLA, HV at SOF).

Regarding your hand baggage allowance, it is the one of the operating carrier for each flight. So pack in such a way you comply with the strictest one (i.e. no accessory).