A letting Agent will normally expect a one year contract. It is expensive to get a letting Agent. They need set up fees which they take from both you -to set up the deposit scheme , sort out a tenancy agreement and do a credit check on Tenants (even if you say no they will do one to cover themselves and its normally around the £150 mark. Then they will take a monthly fee -usually 10% of the monthly rent.
If you want to do it yourself it is relatively easy. All this can be googled so I won't provide links
Download a Short hod Tenancy agreement -some are free some cost around £10.
Do a compare the market for Landlord Insurance . A ten minute job and you can pay online.
Open an online account with these guys
https://www.depositprotection.com
again a 10 minute job once the tenancy agreement has been signed.
And that's it -maybe a couple of hours work for under £50.
I've only used an Agent once when I was abroad with property rented in the Uk and they did very little for the £100 per month they took off me.