boots have a new brand in stock called "naked", which is supposed to be "98%" natural. as far as i remember there was no silocones in it? no SLS anyway, but i found the shampoo must've had something else worse than that because it made my boyfriends scalp realllly flakey. the "intensive care" conditioner sorted out my dry ends for a while though.
a really cheap option for no silicone conditioner is this coconut conditioner they do in pennies. its a big white bottle, costs about 2 euro, i think it smells nice. not too overly coconutty. its not a thick conditioner, but i find it quite good for a while. i use it sometimes to do a "conditioner only" hair wash. i might be wrong about the no silicone thing, someone who knows more about it might correct me, but i'm pretty sure i didn't see any thing ----cone in the ingredients.
other than that, health food shops are a better place for this stuff than boots is.