In August, if you had a car, I would choose to stay (if it was me) in one of the western Dales- possibly Ennerdale, but certainly Wasdale or Eskdale.
Ennerdale Bridge has a couple of nice pubs, and The Gather cafe/community centre, far away from the madding crowds. To be honest I'm not sure if there is a week's worth of walking in Ennerdale, but it's my closest valley, about 6 miles away from me. I may be wrong, there used to be when I went to Scout Camp at Ennerdale- so maybe it's that bit too familiar for me now.
The central Lake District spine (Keswick to Windermere) in August is not for me, good transport or otherwise.
Of Wasdale and Eskdale my preference would be Eskdale- the walking and the scenery is just a bit more 'me'. In Eskdale you can manage without a car. Come up on the coast line train, and then use the L'aal Ratty steam train all week. For inspiration there is Alfred Wainwright's book of walks from the Ratty, which has been republished fairly recently- should be in the Ravenglass and Eskdale shops- I have AW's original version. You could even stay in one of the railway's "camping coaches" at Ravenglass station.
If you need other transport from time to time in Eskdale then Eskdale Taxis (Sim's travel) will be there for you. Sim's are part of the valley- they've been there for ever.
In the Central Lakes, if I was looking for a nice cottage somewhere in mid Summer my choice would be Coniston or Langdale. Coniston is a very good base, with excellent public transport now after the 2025 improvements, plus you have both the Gondola and the lake launch to vary where you go.
Langdale, he says through clenched teeth, due to so much of the property being holiday lets now- Chapel Stile especially. But it is what it is.
The bus service down Great Langdale is even better than Coniston after the 2025 enhancements, and there is every hope the 517 bus down Little Langdale will restart next year.
Another place I might put you in August, closer to Keswick, is Lorton. It's a lot quieter than neighbouring Buttermere with a couple of good pubs but on the three bus routes over Honister- 77/77A/77C
I think you could do a week out west, and a week Coniston/Langdale.
If your heart is set on Keswick my thought would be Borrowdale- Grange in Borrowdale/Seatoller/Rosthwaite. You have the half hourly Open Top Bus for transport and the Lake Launch. I was out in Borrowdale yesterday, on the Open Top Bus (in mid winter, temperatures around freezing). For January I was struck by how busy the bus was and how many people were walking the trails, low and it seemed high level. Rosthwaite would be my village of choice in the Valley. A totally different kind of tourist to those in summer- everyone relaxed and so friendly.
