I'd recommend Prague, it's so cheap yet lacks nothing.
I and another 4 of us stayed just outside the town centre in Krisikova (Prague 8), the food was excellent and cheap, as was the drink! Plenty to do and see and none of it breaks the bank. Eating outside the restaurant is slightly dearer than eating in it though.
We made our own arrangements, Easyjet from Stanstead to Prague was around £80 return, Pension was approx £18 per night including continental brekkie!
Tickets could be bought at the stadium, but they were limited! Buy online and get a choice.
Transport is a breeze, buy a travel card (we paid £7 for a 6 day pass) , the Prague transport system works......................the card is used for buses, trams and metro............unlimited travel within the district.
Trams run frequently and reliably to very near the Marketa from any where in the city. Just a short walk past the Polish Campsite....!! lol ....
Language is NO problem, most Czechs dealing with the public seem to speak English or German
The only pitfall is that August seems to be the rainy season in Praha...........
I'm off to Copenhagen this year for the first time........................