Southgate named a 27-man provisional list for the finals, which will need to be reduced to 23 before the squad head out to Czech Republic in mid-June.
After only losing Manchester United defender Luke Shaw from the core group of players which sealed qualification so convincingly and have since beaten Portugal, Czech Republic and Germany, the head coach feels confident.
"It’s an exciting group of players and we’ve known that for a period of time," he told TheFA.com.
"They’re a tight-knit unit and there are one or two players that we’ve not included before, but who have been doing very well with their clubs and also with us in the junior international teams.
"I’ve got a couple of important decisions to make to take the group from 27 to 23, but I think in terms of the preparation, we’re very pleased.
"We wanted to have challenging friendlies that pitched us against some of the best teams in Europe and we’ve done that and come through them positively.
"So we go with genuine belief in the summer, not just hope."
The loss of Shaw due to injury comes as a disappointment, especially given the player’s involvement in the qualification campaign.
But Southgate revealed he had spoken with United boss Louis van Gaal regarding the player’s availability and that he would not be fit for the competition after a season hit by fitness problems.
"We’ve obviously lost Luke Shaw, which is unfortunate," he explained.
"I’ve spoken with Louis and we’ve monitored Luke, who has always been very keen to come, and Louis has been very supportive of that.
"But medically, he’s not going to be fit and I’ve had that conversation with Louis.
"It’s a shame because Luke has been part of what we’ve done over the last couple of years and it would have been a good experience for him.
"But if he’s the only one that we lose to injury then that will be a real plus for us in terms of our numbers.”
There had been wider debate in the build-up to Southgate’s announcement over the inclusion of players who are eligible for the trip, but have been involved with Roy Hodgson’s senior squad over the past 18 months.
“Roy has been really supportive of what we’re trying to do and he wasn’t going to stop me from picking anybody”
And while Southgate was boosted by the inclusion of U21s regulars Harry Kane, Saido Berahino, John Stones and Calum Chambers, he also explained that he simply chose not to select the likes of Jack Wilshere, Phil Jones, Alex Oxlade-Chamberlain, Raheem Sterling and Ross Barkley.
"It’s not a route we’ve gone down throughout the campaign, as those lads have been with Roy," he said.
"Roy has been really supportive of what we’re trying to do and he wasn’t going to stop me from picking anybody.
"So that was fantastic for him to be as supportive as he was, but we felt all along that those players had served their time with the U21s.
"Yes, we want to win, but we also have to develop the next group that are going to go and push those players and challenge them for their places.
"There are a few players who have been with the seniors before and are now back with us, such as Harry, Saido, John Stones, Jack Butland and Calum Chambers.
England U21s head coach Gareth Southgate speaks about his provisional list for the Euro Finals
"And that’s been a positive thing for the group and all of them who have been with Roy’s squad, it’s really good that they’re of a mindset that they want to go into the Euros and have a real crack at winning this tournament.
"It’s a really positive message for youth development in this country."
Southgate will meet up with his final 23 for the Euros on Monday 2 June, when preparations for the competition will really commence.
The group will spend two weeks training at St. George’s Park and face a final send-off with their game against Belarus at Barnsley on Thursday 11 June, before heading to Czech Republic the following weekend.
Tickets for that game at Oakwell are on sale now, priced at £10 for adults and £5 for concessions.
Call 0871 2266777 or e-mail firstname.lastname@example.org for tickets.