Gemma, congratulations. Taking the two questions in order, and with the caveat that everything below is general and your midwife's answer for you outranks all of it.
On safety: for most healthy, uncomplicated pregnancies, continuing to feed an older child is generally considered compatible with being pregnant, and the guidance on feeding into the second year does not carve out an exception for pregnancy. The worry about miscarriage comes from oxytocin, the hormone released during a feed and also involved in labour contractions. For most of pregnancy the uterus is relatively unresponsive to it, and mild tightenings during a feed are usually harmless. What changes that picture is your own history: a previous preterm birth or late loss, bleeding or uterine pain in this pregnancy, a placental issue being monitored, multiples, or concerns about your own weight and nutrition are all reasons to have a specific conversation rather than assume. That is a question for your midwife or obstetrician at your booking appointment, and Priya is right that the honest answer is that it depends on you.
On the pain: Jess has it. Nipple tenderness is a very common early pregnancy symptom on its own, and feeding on top of it is genuinely hard to tolerate. It is hormonal, not a latch failure, which is why nothing you change seems to help. Expect a marked supply drop later on too, and the milk gradually turning back to colostrum in the second half of pregnancy, which is why toddlers announce that it tastes different. Plenty wean themselves at that point and plenty carry on regardless. All of that, plus what tandem feeding actually looks like afterwards, is in breastfeeding while pregnant.
And Becky's suggestion is a good one that gets overlooked: cutting back to one feed is a real option, not a cop-out. If you do decide to stop altogether, drop one feed at a time and give each change a few days, watching for firm tender patches while your body adjusts, as in stopping breastfeeding.
What I would not do is make this decision inside somebody else's opinion. Get the medical answer from your own midwife, then decide the rest on how it actually feels to you.