Personally, chose both of them HL. Throughout the year, if you find it difficult on one of the subject, then change it to SL. It is harder to change from SL to HL later on the year. if you have HL from the start it would be easier. Worse case scenario, you just change the subject to SL and you need to be ready for the SL test. Both SL papers for chem and bio is easier than HL for sure.