It's absolutely great for your baby to breastfeed, but breastfeeding can be incredibly hard and in some cases there may be a medical reason why it's not possible; or why your baby needs to be given more than just expressed colostrum (latter is v rare). [Before I get yelled at I experienced problems with me first time and problems with baby second time. Still managed to mix feed a bit.]
With the diabetes you will need to control it as well as possible until the birth, but then your baby may be taken to NICU or SCBU to have its blood sugar monitored, and if it looks like going too low they will want to give something to your baby to keep its levels up. This can be sugar water basically, but you need to get started expressing colostrum and then milk too, which can be stored/fed to your baby. The bottles provided by hospitals are single-use old-fashioned style teats. If you want your baby to breastfeed it is worth bringing in some tommee tippee type bottles and teats which are more compatible with breastfeeding. For the first couple of days expressing and feeding is done by hand, into/from a syringe. It's useful to have one person (you) squeezing and your partner collecting the colostrum drops in the syringe.
Hospital will also provide pump (industrial grade, works very well) and and sterilising kit for use in hospital. Then you've got a couple of days to send someone to buy a home kit if needed. My tip is if the hospital pump is Medela, then buy a Medela home pump (not as strong), and take home the personal-use pump attachments (the cone and bottle and bits come sterile for each new patient, so you can take those bits with you and it gives you a spare set so you're not washing the pump constantly. Obviously don't take home the main part of the pump :-)
If you live in the middle of nowhere then it may be worth getting in a couple of single use bottles of ready-made formula, just in case, not the ones that come with old-fashioned teats (same as given out in hospital), I think they're about 79p for 200mls. You pour them into a sterilised tommee tippee bottle.
Support in hospital varies not only from hospital to hospital but midwife to midwife. If you're too poorly post-birth to get out to a bf cafe then call the NCT counsellor as they will come to you in some cases.