I tend to agree with the comments in the first reply, from jaimeelsabio.
It is really good that you will be going midweek. Two months from now? Is that maybe May? Early or late May? Careful of the two Bank Holidays if that is May.
It sounds like an excellent route. Castle Combe, very scenic, if you hit it at the wrong time lots of others will have the same idea as you, and the lanes are very narrow - take your time and get out of the car. By the time you get there you will have become familiar with driving on the left. Just be sure that your navigator tells you if you are too close to the kerb or walls as you drive.
Bibury is also very scenic, and attracts crowds, so much so that a year or two ago a resident parked an old yellow three wheeler car in the middle of the iconic photo scene, and it is very much a one horse town. Once you have seen the Row and the ducks in the river, maybe a cup of tea at the one restaurant, you are done. Very scenic.
Bourton-on-the-Water (don't just call it Bourton, there is a Bouton-on-the-Hill a few miles away, be sure you set the GPS correctly) is a tourist magnet because it is so eye wateringly gorgeous. Parking in the centre can be difficult but there are three slightly hidden additional car parks in addition to the one signposted one. A little persistence can pay off. Well worth a stop in my opinion. I grew up not too far from there and I still return, tourists or not.
As said above, the Slaughters (Upper and Lower) are close by. Don't try driving the ford, use the bridge, unless you really know what you're doing.
Then the short distance to Stow on the Wold. If you can't get parking in the town you can park at the Tesco supermarket just north of the centre for up to 2 hours and a quick stroll back into the centre. Have a look at the stocks, good for a photo op.
Then make your way gently back to Bath. I think you could do worse.
Noting that you will be carrying a munchkin (congratulations!!) I will say that other than Bibury (where the restaurant can assist) the others have public facilities (toilets) that while not the Ritz are all quite serviceable and well signed.
If you are faster than most and have time left over you might consider Chipping Campden (use the whole name, there is a Chipping Norton where Jeremy Clarkson lives nearby, on the way to Oxford, Chipping Campden much more scenic), and or Broadway, with its Tower and Fish Hill. Don't overdo it though...
