Firmness of mattress

I have been looking to buy a new bed for ages but do not know what to buy. All seem comfortable in showrooms but am conscious that that may not be the case 3 weeks on!! I am only 6.5 stone in weight so don't really want anything too firm. I do find Premier Travel Inn beds very comfortable and have been tempted to purchase one from Hypnos, but, again, I am not sure. My husband is double my weight and is happy with our current bed (he too finds the Premier Inn bed comfortable). We currently alternate between two beds - one has a Dreams Kendall mattress (medium comfort grade, 800 pocket spring, no turn memory foam) and the other is a Sleepmasters Sensaform caress (easy care, pocket sprung, memory foam). I have 2 toppers on each mattress but find neither comfortable after about 3 nights. I have been looking at you Origins Comfort 1000 but some advice would be really useful.Many thanks