The Welsh Assembly needs an extra 20 to 30 members to cope with its growing workload, an expert panel has said.
Its report also recommends that 16 and 17-year-olds should be able to vote in assembly elections.
Presiding Officer Elin Jones hoped to see a "stronger, more inclusive and forward-looking legislature".
Welsh Labour said it would not give its view until its 2019 conference, which a Plaid AM said "kills dead" any chance of reform before the next election.
Any changes will require a law to be passed in the assembly with a two-thirds majority.
AMs were given powers to make changes to the way they are elected under the 2017 Wales Act.
Prof Laura McAllister of Cardiff University, who chaired the panel, said the assembly needed more members "to effectively represent the people and communities it serves, hold the Welsh Government to account, and be a parliament that truly works for Wales now and in the future".
"Calling for more politicians is unpopular; but we have to report as we see the evidence," she added.
"As its powers increase, the assembly cannot continue as it is without risking its ability to deliver effectively for the people of Wales."
The panel also recommended a change in the voting system, to a proportional method called the Single Transferable Vote.
One option would be to pair the current 40 constituencies to merge them into 20 seats, each with four AMs, giving a total of 80.
A gender quota would boost the number of women in the Senedd, and the option of standing as a "job share" candidate would aim to encourage people with disabilities or caring responsibilities.
Votes at 16 were also recommended, as long as it was accompanied by "appropriate political and citizenship education".
Prof McAllister said there was "no logical reason" to delay.
Although there would be a "tight timetable", she said it was "do-able" to pass legislation in the summer of 2019.
That would give political parties time to select candidates and allow the Electoral Commission to make any necessary preparations.
Legislation would need a so-called super-majority of two-thirds of assembly members, meaning Labour's support would be crucial.
But Labour said it would not take a decision before its conference in the spring of 2019 after consulting on the proposals next year.
Plaid Cymru AM Simon Thomas claimed Labour's position "kills dead any hope of passing the necessary legislation before the next assembly elections", due in 2021.
Backing calls for a larger legislature, he said: "It makes no sense that our assembly is so much smaller compared with parliaments of comparable size and competence."
Welcoming the report, Presiding Officer Elin Jones said the Assembly Commission - the cross-party group which ordered the study - had already recognised the assembly was "underpowered and overstretched".
"This lack of capacity will not be resolved without bold action, and we cannot afford to ignore it any longer," she said.
She said the commission will consider the proposals and added: "I hope we can find a broad consensus for change and deliver a stronger, more inclusive and forward-looking legislature that works for Wales for many years to come."
Cerys Furlong, chief executive of Chwarae Teg - a charity which promotes the role of women in work - welcomed expansion plans to ease the workload on assembly members and the "strong focus" on boosting the number of women elected.
"Around the world, quotas have been shown to be the most effective means of delivering change at pace, providing the necessary legislative nudge required by some to take action," she said.
Before the report's publication, some politicians questioned the need and public appetite for more assembly members.
UKIP Wales leader Neil Hamilton said the idea should be put to a referendum, saying: "The last thing Wales needs is yet more politicians.
"The assembly costs £55m a year and the increase would mean a budget expansion to over £80m. Do the Welsh people think this is value for money?"
Conservative MP for Monmouth David Davies - a former member of the assembly himself - argued that AMs should work more effectively, rather than see their numbers increase.
But his Labour colleague, Pontypridd AM Mick Antoniw, told BBC Radio Wales: "We have got many assembly members who are working 50, 60, 70 hours [a week]."
"When you start doing that number of hours are you doing that work properly?"