I’ve just booked what looks like a lovely appartment in Lisbon for a week there in July. I recommend http://ferienwohnung-lissabon.de/ Prices seem reasonable and the site has lots of information and photographs, maps etc. The next step s to book a one-way train journey down there via Eurostar and tgv from Paris to the border with Spain where you connect with an overnight sleeper that arrives in Lisbon at 11am (it must go slowly I think). for that seat61.com looks like it provides lots of detailed information and advice though the prices (£59 return on Eurostar London to Paris seems outdated. It looked more like £89 when I visited Eurostar.