3-6 month for prof. Garden designer & 9yo

Waiting to purchase a rustington property and currently living with parents. Looking for private annex or similar, furnished/unfurnished, for short term that allows partner to stay for occasional weekends. Son lives with father every other weekend and would consider sharing one bedroom with son when at home. I work in Chichester 3 days per week and from home for 2. Within 15 /20mins of Rustington. Willing to help with garden! Garden designer/gardener and arborist. Well behaved 9 yr old son. Up to £1k inc bills budget.