Sheepskin is fine all year round - wool is a natural insulator keeping baby warm in cold weather and in hot weather wool absorbs moisture which is then released into the air (keeps them drier). I used them in Australia in the middle of summer (in temps exceeding 36C) and never had a problem with them. Have yet to try it out in HK.
Don't use sheepskin, ELT, as your baby has eczema. Sheepskins, or any animal skins, harbour tons of dustmites. Our allergist told us to pack our beautiful lambskin rugs away or risk our daughter developing wheezing and/or early allergy to dustmites.
They are fantastic. Comfortable and do not retain heat they keep baby's cool and comfortable, better than the synthetic fabric on the push chair. Also natural fibre sheepskin has better moisture retention and softer.