First, please don't go to Poundland for your shampoo – even if it says on the bottle "everything free" there is nothing good inside the shampoo for £1-5.
Second, you can always buy aftercare at my studio! I have amazing professional aftercare that helps to keep treatment stay longer and your hair look healthier.
Third, try to avoid sodium laureth/ laurel sulfate this component quite aggressive and can strip treatment from your hair - the only exemption – professional shampoos – mostly they will contain sulfates but nothing to worry, they will be softened by conditioning components!
Well, "Elena, what's the best one?!" — and here I dont know the answer — all the hair different and need different aftercare! You will need to try few (or maybe a lot) to find the right one for you!
You had your perfect treatment but how to keep it's long as possible? Here the trick — as better aftercare you use as longer treatment will stay as it helps to keep all the goodies we just put inside!