You can check fixtures at espnfc.com for example.
You should be able to get tickets for Chelsea-Maribor, but it might be a rather one sided game. Tickets are GBP 35.
On the 21st there is a full program in the Championship (the second highest league). In London I see Charlton and Brentford. The latter is near the Thames on the flight path into LHR from the east and features advertising on the roof. (You also see Craven Cottage/ Fulham and sometimes Chelsea too). Brentford's ground is famous for having a pub in every corner of the stadium structure.
I have been to Charlton. Nice stadium.
I think you might get a flavor for real, old school football than the oligarch funded Chelsea playing against a hapless Slovenian outfit. There is also Watford playing at home, which is in the northern suburbs. They were a top team in the 1980s when Elton John funded them.