Buying one full Ethereum on the Coinbase exchange Query

[KeMac16]

Hello everyone - I am new to this and have only just started buying my first coins. I wanted to ask: How can I buy a full ethereum coin on the coinbase exchange without having to put the price in which seems to change by the minute? I bought one which ended up with 0.97% of the coin. There was a fee but it seems to me the problem is having to physically put the amount in rather than pressing a box that says something like "purchase one full ethereum"?
Thanks
KeMac16