First step can be to contact a local airgun club, most have Chrono's and a wealth of good advice regarding power levels etc. You will very likely be able to use a club unit, and be able to obtain a choice of pellets at a reasonable charge, or no charge.

If you would be happier with your own, the Combro Chrono is ideal for personal use. It's small, easy to use and inexpensive at about £40.
You will also benefit from their legendary after sales service.
Do a search on here for "Combro", its been done recently.
It's available direct from Here or most of the retailers.

Richard