I'm looking for a gardener that can help me get a decent lawn and advise on suitable plants for my garden, as well as carry out general garden maintenance.
Whats is currently wrong with your lawn ? If it gets water logged in winter then look to try hollow tine it and fill the holes with sand to aid drainage and lessen the effect of any compaction. Apply weed and feed in the next few weeks and scatter new seed to thicken.
Many plants will be suitable, it depends on what style you are trying to create and how much of an effort you are willing to put into creating a micro climate and if you are willing to over winter tender plants, as well as personal preference. Do you want to create a cottage garden with traditional plants like Roses and Foxgloves or an exotic / jungle garden with large foliage plants like Tetrapanaz papyrifer 'rex', hardy bananas (Musa Bajoo) and palms (Chamaerops Humillis, Trachycarpus Fortunei).
Basically ask yourself what you are looking for, if you want to sit in your garden and imagine you are on holiday then you will different types of plants.