hi mamadiva, I really like your description. It gives enough information and makes you sound sincere and trustworthy.
The postage is too high, I'm afraid. I did a search on 'Completed Listings' and those that sold don't generally have postage that exceeds £5 - so agree with flight there.
You don't need to send by first class. 2nd class packets is fine. I assume the snuggle with packaging won't exceed 1 kg (the max weight for 2nd class). Postage for that is £2.49 + £0.72 if you want recorded delivery (I don't bother but it is good practice) + cost of packaging (which can just be a plastic bag cellotaped together and wrapped in brown paper). You will easily come within £5.
For the title, you might want to put the words 'footmuff', 'cosytoes'. It might read a little strange but some people search by using these keywords, rather than 'buggy snuggle' and you want your listing to get on their radar.
The starting price is a little high I feel. I think your item is attractive and if you feel the same, you might want to start at a lower price to encourage a bidding war. To start at £10 means your item will probably sell around £10 or a bit higher because people give your item a miss to hold out for a bargain.
I would suggest not more than a £5 starting price. Again, I say this looking at Completed Listings of auctions of buggy snuggles that achieved a good final price (£25 or more).
Also, I don't think it is good idea to end your listing at 4 pm-ish. You need to end your auctions around 7 pm or later when most people are in. The usual recommendation is to end on a Sat or Sun night but those nights are usually jammed with listings so you get less exposure, even if the traffic is higher.
I find Wed night works equally well by baby-type listings because parents start looking once their little ones are in bed.
Phew, I will stop now.