You would enjoy the Spanish Basque country. Fly to Bilbao or Biarritz. If you fly to Bilbao you can get a very simple and cheap regular bus from the small airport straight to the city centre in about 20 minutes.
The city is lovely for sightseeing; you can walk along the river bank, around the old town, and there are loads of great and inexpensive places to eat, at all times of day. Basque pintxos are exquisite, there's great fish and dairy produce, and the local Txakoli wine and northern Spanish ciders are all well worth a taste. Spanish people love children and will make your baby very welcome; it's normal to come out for dinner or drinks or a walk, ice-cream etc. with the baby sleep in the buggy.
Culture wise you have the Guggenheim gallery, the Bellas Artes, a recently converted small arts' centre called La Alhóndiga, the Basque history museum, and the universities (with parts open to the public).
You can also go to various beaches on the metro (Getxo, Plentzia, Santurtxi) which is quick and cheap. The beach towns are also pleasant.
If you hire a car, you can come from Biarritz airport instead, and also visit a wide range of nearby towns and beaches including beautiful San Sebastián, Lekeitio, Zarautz, and Getaria, and go into the beautiful countryside (including the historic town of Guernika).
Tldr: inexpensive, sunny but not boiling hot (weather is similar to good summer weather on the south coast of U.K.), nice food, nice people, things to look at and mooch around, but no big crowds or hassle.