Look if you've any independent nurseries in your area, these are usually far cheaper than garden centres.
Hi, the first thing im going to say is this,
IF you really think what on seed pkts is for all parts of the country then you are not listening to what ive said,
seed pkt do give a mine of info but they can't give any indication of weather or condition from any one spot on the map in the uk,
Ie southern englad can be a lot warmer in easter than in scotland, so the info on seed pkts needs the experience given by tried and trusted methods,
the exact same thing can and is said via garden centre displays,
ie if for some readon the indoor sections of the unheated dept of a garden centre has lets say cabbage plants growing, they will not continue if you plant them in your garden and it freezes that very same evening,
This is why i said do your home work first via reading all the info you can during the likes of the winter when you have the time to study all the needs of what ever your thinking of growing and you'll find again these readings will tell you what to look for ref weather and conditions the verious plants will need and what they dont need but no book will give you any direct info for your part of the uk,
After all the writers dont know what the weather is going to be like in your area when they write thses books
thats your job to ensure you have the likes of a frost free greenhouse or a building that tends to keep a temature thats above freezing through these cold times,
I keep all my geraniums in my work shop that above my barn ive had this area bothed lined via the walls and ceiling and the tempature stays above 55deg throughout the coldest winter hence the geraniums live in the workshop during the winter and are removed into the greenhouse around march/april time.
Your question was ref what to grow this time of the year and as i said "have a look in any good gardencentre and you'll see whats coming up for future planting,
Now its up to you to plant out your buys when the chance of all frost has gone.
But again you can use verious precautions to help the plants should you get a late frost, ie fleece around the plants, the plastic covers for the likes of individual plants,
But as ive said do your home work before you even buy any plants/shrubs and you'll soon know if your condition are good for what ever your thinking of doing.