pourrais vs pouvais in the text above

Hi Elizabeth, 

The English is -

I could sleep longer = I was able to sleep longer 

which is a past tense and not a conditional.

I would be able to sleep longer = Je pourrais dormir plus longtemps.

Just be aware that 'could' in English can be both but if you can replace it by 'was able to' it will be the imparfait.

Hope this helps!