Do you have National Trust membership? There are a lot of NT car parks that can be expensive if you aren't a member.
If you don't like big walks have a look at Buttermere. It's lovely to walk around. You would need to arrive in the morning before 11am to get easily parked in the car park by the pub. Some people leave their cars anywhere, but we never do that as it risks blocking the road. The drive there is a bit exciting, but DH found it fine as we always go outside school holiday time.
In Ambleside itself Stocks Ghyll is a nice walk right from the centre. We really like Loughrigg Fell, but that might not be what you're looking for.
Elterwater is apparently a lovely walk. We have eaten at Wainwright's Inn near there and it was a great pub, very nice views. I'm October we're planning to walk there from the Elterwater NT car park.
There is the Old Coffin Route from Ambleside to Grasmere. We enjoyed that walk. You could always get the bus back if you're tired. There's a v famous gingerbread shop in Grasmere and lots of cafes.
Derwent Water has lovely surrounding views if you park at Keswick and have a stroll from there (large council run car park in town).
Castlerigg Stone circle just before Keswick is also worth a stop for the views (free on road parking).
Aira Force is another favourite. We haven't been since before covid as they were restricting numbers in the car park, but that's probably relaxed a bit now.
In Ambleside definitely go to The Old Bank House Chocolate Shoppe. Their homemade chocolate is amazing. There is another chocolate shop but it isn't as good (IMHO).
DH really likes a stop at Beer Ambleside to peruse the craft ale. I prefer The Bath House for beautiful toiletries made in Cumbria.
There is a business in Ambleside where you can rent wetsuits, I think it's called Swim I'm The Lakes. They also run swimming courses if I'm remembering correctly.
If you like Japanese food there is a restaurant called Wabi Sabi. Husband and wife run it. We haven't been in yet but saw them on the documentary about Tebay services. The food looked amazing.
The main advice is to always check online in advance where you're planning to park and arrive early to get a spot. There's been so much on bbc 1 north west tonight about visitors abandoning their cars and preventing emergency services from getting through. If you look at LakeDistrict.gov.uk you can see live updates for how busy the car parks are across the national park.