OK. Couple of tips first; preparing your planting area, soil etc. should be done in winter. Start a compost heap for all your garden waste and pretty much anything which was once organic from your household waste - vegetable peelings, newspaper, cardboard. If there are rats in your area consider getting a sealed composting bin for anything a rat might consider edible. I can help more if you wish. The compost you make can be used to improve soil.
Don't buy cheap supermarket compost - it's cheap for a reason. Having said that I buy it BUT I have superb garden compost to mix with it - I use this mixture in pots, troughs etc.
Of the bagged composts I'm familiar with I feel Westland is good. I've used their multi-purpose compost with added John Innes this year and like it. The Jack's Magic is good but is peat based. In your situation you need water retention. I'd suggest the organic Bio Char Carbon Gold. It doesn't contain peat and could, stress could, give better moisture retention.
It's pointless spreading whatever you chose to buy over the whole area. I would look to enrich the individual holes in to which you will put your bedding plants. Dig out your hole with a trowel, mix this soil 50/50 with compost and back fill. Plant your bedding plant.
As an aside can I comment on gardening in general. The horticultural industry has created an image that gardening starts at Easter and finishes in June. This is plain WRONG. It is now, and has been for 20-30 years, a huge issue which has created the public perception gardening happens for 10 weeks a year. When I worked we achieved 70-80% of annual turnover in 10-12 weeks and knew our profit for the year at end of June. It was a nightmare.
My homemade garden compost
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