I have a 4mo baby and 2 older DCs: it is so hard!
You sound like you might want to carry on bf but are finding it near impossible to sustain at the moment, so I'm going to make a few suggestions for you to think about or try in case they help you carry on. At least then if you switch you know you've tried different things and given the decision a bit if time to sink in.
Firstly, remember that there are no guarantees that switching to formula will give you a baby who feeds every 3 to 4 hours - some just want little and often!
Secondly, this was happening to me with my DC3 - feeds might be 2 hours apart in the morning but by late pm it was every 60 mins - but by around 6 weeks old we got a much better feeding pattern going and he started to lengthen it out to 2.5-3 hours most of the time. It really was a short period. And while my older 2 were occasionally a little grumpy there's been no lasting damage to them!
DS never really had a decisive end to feeds and would just bob on amd off for ages. I got him checked for tongue tie and had latch etc checked. All fine so he clearly just liked being on the boob! To try and stretch it out, and give me more freedom with the others, I did a lot of carrying in a sling - I found he was pretty happy near the milk source so I would feed him for a decent time then pop him in the sling while I got on with stuff for the other two.
Get help - someone to hold the baby while you read to the older 2 or someone to do something fun with the older 2. We did a lot if meeting friends to play - exciting for them and another adult to hold the baby while I had a bit if breathing space.
Give the baby to the older 2 for some cuddles. My DS loves sitting with the older 2 (3, now 4, and 6) and it buys me 5 mins to grab a cuppa and is a fun bonding time for them.
We all 4 sit on the sofa together a lot while I feed so I can read to them or watch telly with them or just chat and cuddle them.
If you do mull it over and decide to switch then you have nothing to feel guilty about, but if you do (because us mums are great at beating ourselves up!) then a chat with a breastfeeding counsellor or breastfeeding peer supporter can be excellent as they can help you work through your feelings. In fact, might be worth trying this now to order your thoughts and talk through what you want. I did this when having s rough patch with DC3. Your local NCT can put you in touch with one - NCT BFCs and PSs are trained to be mother-centred in their approach so are as happy dealing with a mum wanting to stop as continue. It's not about changing your decision but helping you work through it all to the right decision for you.
Good luck. I'm 4 months in, knackered as he's a crap sleeper but now doing well with feeding. I wouldn't switch places with you - you're in the hardest bit and it is tough - but want you to know that you will get through it xx