I've always taken advantage of the special offers in GW mag who usually use T & M- although not spring bulbs, their lillies have all grown and been excellent this year despite the weather. Also purchased gladioli and they wouild have done really well if it wasn't for caterpillars eating their leaves
Bulbs like daffs, crocus and tulips I've purchased locally from GC, wilkinson's, Aldi and Lidl - you can see the bulbs and there's no P & P.
Mine have mostly been planted in pots. Planting at the right depth improves the chances of the bulbs growing. FB and B mixed in the compost at the bottom of the pot also helps, along with perlite and a good watering at the time of planting. They are then put in a spot out of direct sunlight and forgotten about until bulbs start appearing in the garden-usually crocus first and then all the pots are brought out from their winter hiding place.
My spring bulbs did really well this year.