I'd wait until the baby is here and book something nearer the time. A 3 month old could be a dream or an absolute nightmare.
My baby was fab and sleeping 8 hours a night at 2 months old. All naps in his cot. We took him out with us to fancy restaurants, he slept through some lovely steak dinners. Easy.
By 3 months he was only sleeping 2 hours at a time, needed rocking for over an hour to get to sleep and cried his eyes out every evening before actually settling. All his naps had to be contact naps. He also had a dairy, soy and egg allergy, which we figured out around 3 months, so my diet was so restricted that eating out was a nightmare. We had a little getaway booked (only an hour drive away) for when baby was 4 months which we cancelled as we would not have been able to enjoy it.
By 6 months he was back to being a dream baby again.
But equally, if baby is easy, you can go crazy and go somewhere further afield, not just Oxfordshire. I have friends who travelled quite a bit with babies that age. They are just very portable. If he/she sleeps fine, the world's your oyster.
Whether or not you're breastfeeding will also make a difference.