I appreciate this decision can feel really frightening and you want to do what is best for your little one.
I am a paediatric registrar and have worked in hospitals treating children and babies for around 5 years.
I have met 2 x families whose children contracted measles as they were not vaccinated. Thankfully the children did recover but were really very ill and needed to stay in hospital for several days and have lots of unpleasant investigations and treatment (because of how ill they were, though measles is a virus they needed also to be treated for possible bacterial infection so lots of needles, blood tests, strong antibiotics, fluids and so on). Those parents immediately changed their minds and were very anxious about getting their children fully vaccinated after the experience.
Unfortunately it was now too late to prevent the measles infection. Measles damages the immune system causing it to forget pathogens the child was already exposed to, so that children who are infected with measles will face years of additional illness. There is also the terrifying but thankfully very rare phenomenon of SSPE.
Parents who choose not to vaccinate are usually very anxious about their child's health and the "what ifs" (which is a big part of the fear of vaccination) so living with the horrible possibility of long term effects which unfortunately cannot be prevented following measles infection is very difficult. I felt really sorry for these parents who did want best for their children but had made a decision they really regretted.
You cannot now rely on herd immunity to protect your child from measles, there are cases of measles in unimmunised children in the UK every year. Very sadly a small number of these children die. There is nothing we can do to treat severe measles other than supportive treatment and covering co-infection with bacteria. We are powerless to prevent measles from severely damaging a child's brain if that is the course it takes.
In contrast to this nearly every child I encounter professionally has had the MMR vaccination with only the expected short term side effects. I cannot recall a single instance of seeing a child in hospital following complications of the MMR vaccination, though the vaccinated children hugely outnumber the unvaccinated. My own two children received the MMR vaccination with no hesitation on my part. I would recommend the MMR vaccination.
Re receiving 3 or more vaccinations at once there is plenty of evidence that this is safe and that it reduces side effects for children vs having the expected side effects from multiple separate immunisations. Vaccinations are not like a typical drug with a dose dependant effect. They involve giving a small part of the infectious organism, inactivated or weakened so that it cannot cause infection, but just enough for the immune system to recognise it and develop a response that will protect the person from the full organism if they encounter it later on. Any reaction the immune system produces to the vaccination (aside from clear cases of allergy to a vaccine precipitant) is a reaction that could happen following infection itself, as the infectious organisms themselves contain the same immune system triggering proteins as the vaccine (that's how vaccines work) but also many additional proteins. You are not avoiding the risk of your child becoming unwell by a reaction of their immune system, by avoiding vaccination. As they are still vulnerable to the exact same reactions following exposure to the infectious organism (and much more).
The way that vaccines work is so different from the way that dose dependant medicines work (eg something that interacts with a receptor and so needs to be proportioned to the number of receptors a person has) that a comparison around dosing doesn't make sense.
I do hope this helps.