Does thickness of mattress for baby cot matter?

Am looking to buy a foam mattress for my newborn’s cot. Planning to get one from Ikea but they come in different thickness ie 5cm, 6cm, 8cm etc. Price-wise, obviously the thicker the more expensive. Saw online that the recommended thickness is 8-10cm. Wondering whether that is true in your experience? Was initially going to just get the 5cm one cos it’s just $30 but now thinking if I should go for at least the 8cm one which is about $70-100.